Doctor of Philosophy in Animal sciences: Utilization of cassava forages for goat production in An Giang province, Vietnam

HUE UNIVERSITY HUE UNIVERSITY OF AGRICULTURE AND FORESTRY LE THI THUY HANG UTILIZATION OF CASSAVA FORAGES FOR GOAT

PRODUCTION IN AN GIANG PROVINCE, VIETNAM

DOCTOR OF PHILOSOPHY IN ANIMAL SCIENCES

HUE, 2020

HUE UNIVERSITY HUE UNIVERSITY OF AGRICULTURE AND FORESTRY LE THI THUY HANG UTILIZATION OF CASSAVA FORAGES FOR GOAT

PRODUCTION IN AN GIANG PROVINCE, VIETNAM

SPECIALIZATION: ANIMAL SCIENCES CODE: 9620105 DOCTOR OF PHILOSOPHY IN ANIMAL SCIENCES SUPERVISOR 1: Assoc. Prof. Nguyen Xuan Ba

SUPERVISOR 2: Dr. Dinh Van Dung

HUE, 2020

DECLARATION

for Rural Development

of Livestock Research

I hereby guarantee that scientific work in this thesis is mine. All results described in this thesis are righteous and objective. They have been published in Journal (LRRD) http://www.lrrd.org

Hue University, 2020

Le Thi Thuy Hang, PhD. Student

DEDICATION

To my parents who taught me the good things in my life, my loving husband and my sons.

ACKNOWLEDGEMENTS

These studies were carried out at An Giang University, Hue University of

Agricultural and Forestry, Hue University with financial support from the Mekong

Basin Animal Research Network (MEKARN II) Project. I am grateful for their support

for the thesis research and the scholarship for the PhD study.

I would like to express my sincere thanks to:

Associate Professor Nguyen Xuan Ba, my main supervisor, for all his ideas,

knowledge and experience. Thanks for unceasing support in research and social

activities. He has given me invaluable support, encouragement and guidance

throughout my study. His reading, editing and follow -up of this thesis are gratefully

acknowledged.

Dr. Dinh Van Dung, my second supervisor, who has given me invaluable

support, encouragement, criticism, excellent skilled technical assistance and guidance

throughout my study.

Professor Thomas R. Preston, who has given me invaluable support, for valuable

advice, encouragement, enthusiasm and discussions throughout the study. His reading

and correcting and follow-up of this thesis from the beginning to the end have enabled

me to accomplish this work successfully, especially in correction of my English.

Associate Professor Le Van An, Rector of Hue University of Agriculture and

Forestry for giving us the best conditions, encouragement and support during our

studies in Hue.

Dr. Khieu - Borin, Regional Coordinator of Mekarn II Project “Vietnam –

SAREC Sustainable Livestock Production Systems” project, for valuable advice and

discussions.

Associate Professor Duong Nguyen Khang, Consultant of the “Vietnam –

SAREC Sustainable Livestock Production Systems”, for valuable advice.

Professors, Lectures and assistant lecturers in courses which I have attended

during my studies for sharing their valuable knowledge.

Associate Prof. Dr. Vo Van Thang, Rector of An Giang University for giving

me permission to study, facilitation and encouragement.

iii

My Dean, Dr. Ho Thanh Binh, Dean of Agriculture and Natural Resources

Faculty of An Giang university for giving me permission to study, facilitation and

encouragement.

My colleagues at the Department of Animal Husbandry and Veterinary

Medicine of Agriculture and Natural Resources Faculty of An Giang University for

performing the chemical analyses and sharing experiences in scientific research and

social activities.

My students, for help me in taking care the experiments.

To my friends in the PhD. Course, from Lao, Cambodia and Vietnam for giving

me a warm and friendly atmosphere

To my big family, for all their support and encouragement throughout my study.

And special thanks to my husband Tran Xuan Hien, two children’s who understood my

work, and shared the happiness and sadness with me, for his loving, unceasing support

and patience for my whole- life study.

ABSTRACT

The aims of the study were to improve utilization cassava forage for increasing

performance and reducing enteric methane emission in goat fed cassava forage

restricted level of brewery grain and biochar in An Giang province, Vietnam. There

were one survey and four experiments in this study.

The survey of cassava and goat systems in Tinh Bien and Tri Ton districts, An

Giang province showed that there is an increasing tendency to plant cassava. At the

same time there are major trends in the population of goats increasing. However, goat

production systems were still extensive, exploiting natural feed resources with small

herds of indigenous goats, which have small sizes and low growth rates. Feed and

feeding for goats were mainly natural grass and by-products, from crop growing, low

nutrition. It is not enough feed in rainy and flooding season. Whole, cassava forage

averaginge 5 tons/ha was available, but the farmers did not use them as feed for goats.

The impact of different levels of urea added to cassava stems (CS) and its

chemical properties was investigated (Experiment 1). The urea treated cassava stems

(UCS) (3% in DM) made good quality ensilage, with no loss in nutritive value that

could be stored up to 8 weeks. An additional benefit was that the urea treatment

reduced the content of HCN in the ensiled stems.

Base on these results of the experiment 1, experiment determined the effect on

feed intake, digestibility and N- retention in goats of supplementing the urea treated

cassava stems (UCS) with fresh water spinach and biochar (Experiment 2). DM

intake was increased 18% by supplementing the UCS with biochar; and by 24% by

addition of water spinach. The combined effect of biochar plus water spinach was to

increase DM intake by 41%. Biochar increased daily N retention by 46% and the

biological value of the absorbed N by 12%. It is thought that this major benefit from

biochar arises from the role it plays as physical support for biofilms acting as habitat

for diverse microbial communities working for the benefit of the host animal and thus

acting as a form of prebiotic.

Experiment 3 describes the addition of increasing levels of brewers’ grains (0 to

6%) in a diet of ad libitum sweet cassava forage for growing goats. The 4% level of

brewers’ grains increased the DM intake, the apparent DM digestibility, the N retention

and the biological value of the absorbed nitrogenous compounds. The methane levels in

eructed gas increased with a curvilinear trend as the proportion of brewers’ grains in the

diet was increased.

The benefits of biochar were tested further in experiment 4. Twelve growing

male goats of the Bach Thao breed, were given a basal diet of ad libitum fresh cassava

forage supplemented with 4% (DM basis) of brewers’ grain. The biochar was supplied

over the range of 0 to 1.5% in diet DM. Responses in feed intake, live weight gain and

feed conversion to biochar followed curvilinear trends with optimum benefits when

biochar was added at 0.86% of the diet DM. By contrast, the eructed methane

production was decreased linearly with level of biochar.

Key word: Cassava stems, cassava forage, brewers’ grain, liveweight gain,

biochar, methane emission

DECLARATION .............................................................................................................. i

DEDICATION ................................................................................................................. ii

ACKNOWLEDGEMENTS ............................................................................................ iii

ABSTRACT ..................................................................................................................... v

TABLE OF CONTENTS .............................................................................................. vii

LIST OF FIGURES ....................................................................................................... xii

LIST OF TABLES ........................................................................................................ xiv

LIST OF ABBREVIATIONS, SYMBOLS AND EQUIVALENTS ................................. xvi

INTRODUCTION ............................................................................................................ 1

1. PROBLEM STATEMENT ........................................................................................... 1

2. AIMS AND OBJECTIVES OF THE STUDY ............................................................. 2

2.1. THE AIMS OF THE STUDY ................................................................................... 2

2.2 OBJECTIVES OF THE STUDY................................................................................ 2

3. RESEARCH HYPOTHESES ....................................................................................... 2

4. SIGNIFICANCE/INNOVATION OF THE DISSERTATION.................................... 3

4.1 SCIENTIFIC SIGNIFICANCE .................................................................................. 3

4.2. PRACTICAL SIGNIFICANCE ................................................................................ 3

CHAPTER 1 OVERVIEW OF RESEARCH ISSUES .................................................... 4

1. GOAT PRODUCTION SYSTEMS IN AN GIANG.................................................... 4

1.1 GEOGRAPHICAL LOCATION AND CLIMATE IN AN GIANG ......................... 4

1.2. GOAT RAISING SYSTEMS IN AN GIANG .......................................................... 4

1.2.1 Goat population and management ........................................................................... 4

1.2.2. Feed and feeding management for goat .................................................................. 7

1.3. OPPORTUNITIES AND CHALLENGE FOR GOAT PRODUCTION .................. 9

2. THE DIGESTIVE SYSTEMS AND ENTERIC METHANE EMISSION IN

RUMINANTS................................................................................................................. 11

2.1. RUMEN FERMENTATION AND METHANE PRODUCTION .......................... 11

2.1.1. Rumen fermentation ............................................................................................. 11

2.1.2. Volatile fatty acids pattern .................................................................................... 12

2.1.3. Protein metabolism ............................................................................................... 13

2.2. METHANE PRODUCTION ................................................................................... 14

2.2.1. Pathway of methane production ........................................................................... 14

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2.2.2. Manipulation in mitigation of methane production .............................................. 16

3. POTENTIAL OF CASSAVA FORAGE FOR GOAT PRODUCTION .................... 19

3.1. PLANT AREA AND DISTRIBUTION OF CASSAVA AND YIELD OF

CASSAVA IN VIETNAM, AN GIANG ....................................................................... 19

3.2. POTENTIAL OF CASSAVA FORAGE FOR GOAT PRODUCTION ................. 21

3.2.1. Proportion yield of parts of cassava forage ......................................................... 21

3.2.2. Composition of cassava forage, parts of cassava forage ...................................... 21

3.2.3. Using cassava foliage for goat production ............................................................ 21

3.2.4. Antinutritional factors (Tannin and HCN) of cassava forage ............................... 22

3.2.5. Reducing methods antinutrients factor in cassava foliage ................................... 24

4. IMPROVING GOAT PRODUCTION AND REduction of METHANE EMISSION

PRODUCTION............................................................................................................... 26

4.1. IMPROVING STRATEGY GOAT PRODUCTION .............................................. 26

4.2. CLIMATE CHANGE AND REduction of METHANE EMISSION

PRODUCTION............................................................................................................... 27

5. CONCLUSIONS ........................................................................................................ 29

CHAPTER 2 EVALUATION OF THE POTENTIAL OF CASSAVA forage AS FEED

FOR GOATS IN AN GIANG PROVINCE, VIETNAM ............................................... 42

1. INTRODUCTION ...................................................................................................... 42

2. MATERIALS AND METHODS ............................................................................... 43

2.1. THE FOLLOWING INDICATORS WERE USED IN THE INVESTIGATION OF

THE SURVEY ................................................................................................................ 43

2.2. DATA COLLECTION AND CALCULATION ..................................................... 44

2.3. CHEMICAL ANALYSIS ........................................................................................ 45

2.4. STATISTICAL ANALYSIS ................................................................................... 45

3. RESULTS AND DISCUSSION ................................................................................. 46

3.1. CASSAVA PRODUCTION IN AN GIANG PROVINCE ..................................... 46

3.1.1. The production and yiled of cassava .................................................................... 46

3.1.2. Plant area of cassava by district from 2014-2017 ................................................. 46

3.1.3. Yield of cassava with different of variety in An Giang ........................................ 48

3.1.4. Planted area and the purposes of cassava cultivation ........................................... 48

3.1.5. Evaluation of chemical composition of cassava parts .......................................... 50

3.1.6. The fresh and dry yield of cassava proportion with different variety .................. 50

3.2. GOAT PRODUCTION IN AN GIANG PROVINCE............................................. 51

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3.2.1. Ruminants population in An Giang from 2014- 2017 .......................................... 51

3.2.2. Goat farm size and purpose raising in An Giang province ................................... 52

3.2.3. Goat prodution systems in An Giang .................................................................... 53

3.2.4. Feed and feeding systems ..................................................................................... 54

3.2.5. Diseases and diseases management ..................................................................... 55

4. CONCLUSIONS ........................................................................................................ 56

CHAPTER 3 USING UREA TO TREAT CASSAVA STEMS AND EFFECT OF

WATER SPINACH AND BIOCHAR ON FEED INTAKE, DIGESTIBILITY AND N-

RETENTION IN GOATS FED UREA TREATED CASSAVA STEMS ..................... 60

1. INTRODUCTION ...................................................................................................... 61

2. MATERIALS AND METHODS ............................................................................... 63

2.1. EXPERIMENT 1 ..................................................................................................... 63

2.2. EXPERIMENT 2 ..................................................................................................... 64

3. RESULTS AND DISCUSSION ................................................................................. 68

3.1 EXPERIMENT 1 ...................................................................................................... 68

3.1.1 Hygienic quality of cassava stems treated by physical evaluation ........................ 68

3.1.2. Chemical compositions of cassava stems treated with difference levels of urea

and stored times .............................................................................................................. 70

3.2. EXPERIMENT 2 ..................................................................................................... 76

3.2.1. Composition of the diet ingredients ...................................................................... 76

3.2.2. Feed intake and digestibility ................................................................................. 77

3.2.3. Nitrogen retention ................................................................................................. 80

4. CONCLUSIONS ........................................................................................................ 82

CHAPTER 4 EFFECT OF DIFFERENT LEVELS OF BREWERS’ GRAINS

SUPLEMENTATION ON PERFORMANCE AND METHANE EMISSION OF

GOATS FED CASSAVA FORAGE .............................................................................. 87

1. INTRODUCTION ...................................................................................................... 87

2. MATERIALS AND METHODS ............................................................................... 88

2.1. EXPERIMENTAL DESIGN ................................................................................... 88

2.2. ANIMALS AND MANAGEMENT ........................................................................ 88

2.3. FEEDS AND FEEDING ......................................................................................... 89

2.4. DIGESTIBILITY AND N RETENTION ................................................................ 89

2.5. RUMEN PARAMETERS ....................................................................................... 89

2.6. RUMEN GAS EMISSIONS .................................................................................... 90

2.7. ANALYTICAL PROCEDURES............................................................................. 90

2.8. STATISTICAL ANALYSIS ................................................................................... 90

3. RESULTS AND DISCUSSION ................................................................................. 90

3.1. COMPOSITION OF DIET INGREDIENTS .......................................................... 90

3.2. FEED INTAKE AND DIGESTIBILITY ................................................................ 91

3.3. RUMEN PARAMETERS ....................................................................................... 93

3.4. NITROGEN RETENTION ..................................................................................... 94

3.5. LIVE WEIGHT GAIN AND FEED EFFICIENCY ................................................ 96

3.6. METHANE EMISSIONS ........................................................................................ 98

4. CONCLUSIONS ........................................................................................................ 99

CHAPTER 5 EFFECT OF BIOCHAR SUPPLEMENTATION LEVELS ON

GROWTH AND METHANE EMISSIONS OF GOATS FED FRESH CASSAVA

FORAGE ...................................................................................................................... 102

1. INTRODUCTION .................................................................................................... 102

2. MATERIALS AND METHODS ............................................................................. 103

2.1. LOCATION AND DURATION ........................................................................... 103

2.2. EXPERIMENTAL DESIGN ................................................................................. 103

2.3. FEEDING AND MANAGEMENT ....................................................................... 104

2.4. MEASUREMENTS ............................................................................................... 105

2.5. ERUCTED GAS EMISSIONS AND ANALYSIS ............................................... 106

2.6. ANALYTICAL PROCEDURES........................................................................... 106

2.7. STATISTICAL ANALYSIS ................................................................................. 106

3. RESULTS AND DISCUSSION ............................................................................... 107

3.1. COMPOSITION OF DIET INGREDIENTS ........................................................ 107

3.2. FEED INTAKE ..................................................................................................... 107

3.3. GROWTH AND FEED CONVERSION .............................................................. 108

3.4. METHANE EMISSION ........................................................................................ 111

4. CONCLUSIONS ...................................................................................................... 113

CHAPTER 6 GENERAL DISCUSSION AND CONCLUSIONS .............................. 117

1. GENERAL DISCUSSION ....................................................................................... 117

1.1. POTENTIAL OF CASSAVA IN VIETNAM ....................................................... 117

1.2 EFFECT ON NUTRITIVE VALUE OF CASSAVA (MANIHOT ESCULENTA

CRANTZ) STEMS OF ENSILING THEM WITH UREA ........................................... 118

1.3 DIGESTIBILITY, NITROGEN BALANCE AND METHANE EMISSIONS IN GOATS

FED CASSAVA FORAGE AND RESTRICTED LEVELS OF BREWERS’ GRAINS .... 118

1.4 EFFECT OF BIOCHAR AND WATER SPINACH ON FEED INTAKE,

DIGESTIBILITY AND N-RETENTION IN GOATS FED UREA-TREATED

CASSAVA STEMS ...................................................................................................... 119

1.5. EFFECT OF BIOCHAR ON GROWTH AND METHANE EMISSIONS OF

GOATS FED FRESH CASSAVA FORAGE. ............................................................. 120

2. GENERAL CONCLUSIONS ................................................................................... 120

3. IMPLICATION AND FUTHER RESEARCH ........................................................ 121

3.1 IMPLICATIONS .................................................................................................... 121

3.2 FUTURE RESEARCH ........................................................................................... 122

PUBLICATION LIST .................................................................................................. 126

LIST OF FIGURES

Figure 1.1. Number of goats in An Giang from 2012 -2017 ............................................ 4

Figure 1.2. Distribution of goat by district in An Giang, 2017 ........................................ 5

Figure 1.3. Farmers buy grass from another region .......................................................... 8

Figure 1.4. Microbes needed for fermentation (Leek, 1993) .......................................... 11

Figure 1.5. Metabolic pathways of VFA (Bergman, 1993) ............................................ 12

Figure 1.6. The reaction of methane generation ............................................................. 15

Figure 1.7. Plant area of cassava in Vietnam, 2017 ........................................................ 19

Figure 2.1. Cassava plant parts ....................................................................................... 45

Figure 2.2. Cassava forage parts ..................................................................................... 45

Figure 3.1. Freshly harvested cassava stems .................................................................. 64

Figure 3.2. Chopping into 5-10 cm lengths .................................................................... 64

Figure 3.3. Urea added at 3% of stems DM ................................................................... 64

Figure 3.4. Chopped stems-urea are put in polyethylene bags and the air extracted ..... 65

Figure 3.5. Urea-treated stems are stored for 21 days .................................................... 65

Figure 3.6. Urea-treated stems after 21-day storage ready for feeding .......................... 65

Figure 3.7. The biochar was the residue from rice husks used as fuel in a gasifier stove

(Olivier) .......................................................................................................................... 66

Figure 3.8. Biochar, water spinach and urea-treated cassava stems were fed in separate

troughs ............................................................................................................................ 66

Figure 3.9. Supplements of water spinach and biochar increased DM intake by goats

fed urea-treated cassava stems ........................................................................................ 79

Figure 3.10. Effect of water spinach on DM digestibility in goats fed urea-treated

cassava stems with or without a supplement of biochar ................................................. 80

Figure 3.11. Effect of biochar on DM digestibility in goats fed urea-treated cassava

stems with or without a supplement of water spinach .................................................... 80

Figure 3.12. Effect of water spinach on N retention in goats fed urea-treated cassava stems

with or without a supplement of biochar ........................................................................... 81

Figure 3.13. Effect of biochar on N retention in goats fed urea-treated cassava stems

with or without a supplement of water spinach .............................................................. 81

Figure 3.14. Effect of water spinach on N retention as % of digested N in goats fed

urea-treated cassava stems with or without a supplement of biochar ............................. 81

xii

Figure 3.15. Effect of biochar on N retention as % of digested N in goats fed urea-

treated cassava stems with or without a supplement of water spinach ........................... 81

Figure 4.1. Relationship between dry matter inatke and different level of brewers’ grain

in goats fed cassava forage. ............................................................................................ 92

Figure 4.2. Correlation between the differnce level of brewers’ grains and apparent

digestibility of DM and CP ............................................................................................... 93

Figure 4.3. Relationship between different levels of brewers’ grains and rumen

ammonia before and after offering new morning feed. .................................................. 94

Figure 4.4. Relationship beween of dietary level of brewers’ grains and N retention as a

percentage of N digested ................................................................................................ 95

Figure 4.5. Relationship between live weight gain and different levels of brewers’

grain in goats fed cassava forage. ................................................................................... 97

Figure 4.6. Effect of level of brewers’ grains on DM feed efficiency ............................ 97

Figure 4.7. Effect of increasing intake of brewers’ grains on the methane: carbon

dioxide ratio in mixed air-expired breath of the goats fed a basal diet of fresh cassava

forage. ............................................................................................................................. 98

Figure 5.5. Curvilinear response of DM intake of goats to percent biochar in a cassava

forage diet with the optimum level at about 0.8 % biochar in DM .............................. 108

Figure 5.6. Curvilinear response of live weight gain of goats to percent biochar in a

cassava forage diet with the optimum level at about 0.86 % biochar in DM ............... 110

Figure 5.7. Growth response curves to biochar with water retention capacities of 3.81

and 4.89 fed in succeeding periods (-15 to + 10 days) and 10-90 days) ...................... 110

Figure 5.8. Linear reduction in methane: carbon dioxide ratio in eructed gas of goats

fed up to 1.3% biochar in a diet of cassava forage ....................................................... 112

Figure 6.1. Forage and stems that remain when the cassava roots are harvested ......... 117

xiii

LIST OF TABLES

Table 1.1. The chemical composition of cassava forage variety .................................... 21

Table 1.2. Tannin and HCN content of cassava foliage ................................................. 24

Table 2.1. Plant area of cassava in An Giang from 2014-2017 ...................................... 46

Table 2.2. Plant area of cassava in An Giang province .................................................. 48

Table 2.3. Yield of cassava with different variety in 2017 ............................................. 48

Table 2.4. Plant area of cassava cultivation in An Giang ............................................... 49

Table 2.5. Chemical composition of cassava parts ......................................................... 50

Table 2.6: Yield of cassava proportion with different variety ........................................ 51

Table 2.7. Population of ruminants in An Giang from 2014- 2017 ............................... 52

Table 2.8. Farm size and purpose raising ...................................................................... 53

Table 2.9. Goat production systems in Tri Ton and Tinh Bien district .......................... 53

Table 2.10. Feed and feeding systems for goats in Tri Ton and Tinh Bien district ....... 55

Table 2.11. Diseases and diseases management of goats .............................................. 56

Table 3.1. The chemical composition of cassava stems before treating in experiment 164

Table 3.2. The layout of the experiment ......................................................................... 65

Table 3.3. Effect of urea level and storage time on pH in cassava stems ....................... 69

Table 3.4 : Effect of urea level and storage time on ammonia in cassava stems ............ 70

Table 3.5. Effect of urea level and storage time on HCN (mg/kgDM) content of

cassava stems. ................................................................................................................. 71

Table 3.6. Effect of urea level and storage time on tannins in cassava stems ................ 72

Table 3.7. Effect of urea level and storage time on DM of cassava stems .................... 73

Table 3.8. Effect of urea level and storage time on crude protein in cassava stems ...... 74

Table 3.9. Effect of urea level and storage time on NDF in cassava stems ................... 75

Table 3.10. Effect of urea level and storage time on ADF in cassava stems. ................. 76

Table 3.11. Chemical composition of diet ingredients (UCS is urea-treated cassava

stems) in experiment 2 .................................................................................................... 77

Table 3.12. Effect of biochar and water spinach on feed intake ..................................... 78

Table 3.13. Effect of water spinach and biochar on nutrient digestibility (%) in goats

fed urea treated cassava stems ........................................................................................ 79

Table 3.14. Nitrogen balance in goats fed urea-treated cassava stems supplemented

with or without fresh water spinach and biochar. ........................................................... 80

Table 4.1. The layout of the experiment ......................................................................... 88

xiv

Table 4.2. Composition of diet ingredients .................................................................... 91

Table 4.3. Feed intake in goats fed cassava forage supplemented with different levels of

brewers’ grains ................................................................................................................ 91

Table 4.4. Nutrient digestibility (%) in goats fed cassava forage supplemented with

different levels of brewers’ grains .................................................................................. 93

Table 4.5. Protozoa numbers, ammonia and pH in rumen fluid, before and 4h after,

offering fresh feed in the morning .................................................................................. 94

Table 4.6: N balance (g/day) in goats fed cassava forage supplemented with different

levels of brewers’ grain .................................................................................................. 95

Table 4.7. Live weight gain and feed efficiency in goats fed cassava forage

supplemented with different levels of brewers’ grain .................................................... 96

Table 4.8. Mean values for the ratio methane: carbon dioxide in mixed eructed gas and

air in the plastic-enclosed chambers where the goats were enclosed over ten minutes

periods ............................................................................................................................. 98

Table 5.1. Composition of diet ingredients .................................................................. 107

Table 5.2. Feed intake in goats fed increasing levels of biochar in a diet of fresh

cassava forage .............................................................................................................. 108

Table 5.3. Live weight and feed conversion in goats fed increasing levels of biochar in

a diet of fresh cassava forage ........................................................................................ 109

Table 5.4: The ratio methane: carbon dioxide in eructed gases from goats fed cassava

forage supplemented with biochar ................................................................................ 111

LIST OF ABBREVIATIONS, SYMBOLS AND EQUIVALENTS

Acid detergent fiber ADF

Adenosine triphosphate ATP

Body weight BW

Brewery spent grain BSP

Crude protein CP

Condensed tannins CT

Cyanogenic potential CNP

Methane CH4

Carbon dioxide CO2

Dry matter DM

Eggs per gram EPG

Fresh weight FW

Green house gas GHG

Self-produced polymeric substance EPS

Hydrolysable tannins HT

Hydrogen cyanide HCN

Live weight LW

Nitrogen N

No detection ND

Neutral ditergent fiber NDF

Short -chain fatty acid SCFA

Total mix ration TMR

Volatile fatty acid VFA

Water retention capacity WRC

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INTRODUCTION

1. PROBLEM STATEMENT

An Giang province in the South of Vietnam, is a watershed province in the

Mekong Delta, and one of the largest cultivated areas in the Mekong Delta. The total

area of agricultural land is more than 282,676 ha, of which paddy land accounts for

85.2% (Statistic yearbook of An Giang, 2018). An Giang is one of the two provinces in

the Mekong Delta with hills and mountains, mostly in the northwest of the province, in

Tinh Bien and Tri Ton districts. This is the last mountain cluster of the Annamites, so

the geological features also have similarities with the Southern Truong Son. An Giang

has a tropical monsoon climate, with two distinct seasons: rainy season and dry season.

The temperature ranges from 200C to 360C and rainfall from 1400 to 1600 mm. The

rainy season is the least in February and the highest in September. The average

humidity is 75-80% (An Giang hydrometeorological Station, 2017). Due to the

topography, the land resources are divided into different types: alluvial soil, alkaline

soil, mountainous land. Total area of hilly land in An Giang is about 29,320 ha,

accounting for 8.6% of total land area of the province. Agricultural cultivation in this

mountainous area is not favorable because of its low productivity, lack of water for

irrigation in the dry season, but when the rainy season comes, some districts are

affected by floods eg: the flooding in 2018 affected hundreds of hectares of rice and

crops in the Mekong Delta. As Naqvi and Sejian (2011) showed droughts, flooding and

depletion of natural resources, were caused by global climate change. Therefore, goat is

one of animal species, selected to keep with its advantagous characteristics of low

water consumption, drought resistance and browsing behaviors adapting to feeds from

plants adapting to the sea water. Besides, goat production in An Giang has developed in

recent years. The number of goats were 13,950 head in 2017 (Statistic yearbook of An

Giang, 2018). Nguyen Binh Truong (2016) showed that in An Giang province, goats

were raised mainly in small scale and intensive systems for meat production; breeding;

and meat. Normally, feed for goats is from natural resources and by-products of the

season such as sweet potato, banana leaf, water spinach, lipstick around the house,

settling idle work, bringing economic efficiency to farmers. Some separate supplement

feeds are used such as coconut cake, soybean extraction meal, brewery waste, soya

waste, rice bran, etc., and concentrate is also supplemented with protein and energy

sources in diets (Nguyen Van Thu, 2016). The goat raisers in this area are spontaneous,

under-invested, using local breeds, natural grass, not enough nutritional value for goat,

so the meat quality is not high. But cassava is a potential, and plentiful, source of food

for ruminants but the farmers in An Giang do not use it.

Based on the above problems and threats, we hypothesize that utilization of

cassava forage for improving goat production and reducing enteric methane emission

from goat production in An Giang province, Vietnam. This study was designed to test

the hypothesis by addressing the following specific aims were to improve nutritive

value of cassava stems and stored by urea treatment. In addition, using brewers’ grain

and biochar supplied to improve growth rate and reduce methane emissions in a basal

diet of cassava forage fed to growing goats.

2. AIMS AND OBJECTIVES OF THE STUDY

2.1. THE AIMS OF THE STUDY

The overall aim of this thesis was to improve utilization of cassava forage for

increasing performance and reducing enteric methane emission from goat production in

An Giang province, Vietnam.

2.2 OBJECTIVES OF THE STUDY

The present study objectives were:

- To evaluate the potential productivity and nutritive value of cassava stems, and

cassava forage for goats in An Giang Province.

- To determine level of urea addition to cassava stems for storage to improve

nutritive value, especially its digestibility

- To examine the effect of biochar supplementation on feed intake, digestibility,

N retention in goats fed urea treated cassava stems

- To determine levels of brewery grain that affect feed intake, digestibility and

growth in goats fed sweet cassava foliage as basal diet.

- To determine levels of biochar that would reduce methane production in goats

fed a basal diet of fresh cassava foliage and brewery grain.

3. RESEARCH HYPOTHESES

The hypotheses tested were that:

- Cassava forage will have potential as a by-product for developing goat

production in An Giang.

- Using urea to treat cassava stems will improve nutritive value and storge long

time for feeding yearround.

- Supplementation with both water spinach and biochar will improve feed intake

and its digestibility in goats fed a basal diet of urea treated cassava stems.

- Adding up to 6% of brewery grain will improve feed intake, digestibily, growth

and reducing toxicity of the HCN in goat fed a basal diet of fresh cassava forage.

- Adding biochar will reduce methane emissions and increase liveweight in goat

fed a basal diet of fresh cassava forage and brewery grain. (the best level of brewery

grain in previous experiment).

4. SIGNIFICANCE/INNOVATION OF THE DISSERTATION

4.1 SCIENTIFIC SIGNIFICANCE

The thesis contributes to the science of:

- Using urea to treat cassava stems is one of method to increase nutritive value,

reduce HCN content and can be storeed at least 8 weeks.

- Adding 4% brewery grain and 0.86% biochar (DM based) in Bach Thao

goat’s diet, that is basal of fresh cassava foliage has improved growth and reduced

enteric methane emission from goat production.

4.2. PRACTICAL SIGNIFICANCE

- The results of the study are of scientific value for managers, researchers,

universities, graduate students and agricultural students’ references.

- The present results of show that adding urea to cassava stems can provide

storage to use as feed goat for year around, specially in flooding or rainy season.

- The study results of the dissertation serve as a scientific basis for businesses

and husbandry to use and coordinate goat diets towards reducing methane emissions.

- Introducing cassava forage as goats feed, reducing the HCN content,

improving growth and reducing methane emission with supplementing additive as

brewery grain and biochar.

CHAPTER 1 OVERVIEW OF RESEARCH ISSUES

1. GOAT PRODUCTION SYSTEMS IN AN GIANG

1.1 GEOGRAPHICAL LOCATION AND CLIMATE IN AN GIANG

An Giang is a watershed province in the Mekong Delta, with an area of 3,536.8

km2, part of the Long Xuyen Quadrangle. which is one of the largest cultivated areas in

the Mekong Delta. The province is bordered by Cambodia to the northwest (104 km),

to the south-west by Kien Giang province (69,789 km), to the southeast by Can Tho

city (44,734 km), to the east by Dong Thap province (107,628 km). An Giang in the

geographical latitude of about 10 to 110 North latitudes, ie, close to the equator, so

temperature and precipitation are similar to the equatorial climate. There are two

seasons in An Giang province: dry season (from December April), and rainy season

(from May to November), in this time there is flooding season (from August to

November). Normally, when flooding comes, the field area is immersed by flooding, it

is difficult finding feed and there was not enough feed for ruminants or goat production

in this area.

1.2. GOAT RAISING SYSTEMS IN AN GIANG

13,950

11,905

7,876

) s d a e h ( t a o g

f o

4,325

3,006

2,346

r e b m u N

16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0

2012

2013

2014

2015

2016

2017

1.2.1 Goat population and management

Year

Figure 1.1. Number of goats in An Giang from 2012 -2017

Source: Statistic yearbook of An Giang, 2018

In recent years goat production in Vietnam has been developed very fast around

30.0% annually with the total population of 2,556,300 heads in 2017, due to high

demand of goat meat for consumption. Some projects of goat production funded by

Oxfam UK, associated with Mekong delta provinces, which show the effective

production contributing to the poor alleviation and prosperous income. In An Giang,

goat production in 2017 was 13,950 heads, that is 6 times higher than the number of

goats in 2012, which shows that the trend of goat production in An Giang gradually

develops, the farmers are interested in and develop goat husbandry. In recent years,

consumers have been more interested in nutritious food sources from goat meat, goat

meat market has increased, and the goat meat prices have also increased, but goat

farming is low investment, easy to manage, less risky, more diversified feed than other

ruminants like cattle. Therefore, raising goats will help farmers to earn higher profits.

- Distribution of goat by district in 2017

GOAT

Chau Đoc city, 234

Long Xuyen City, 428

Thoai Son, 719

An Phu, 840

Cho Moi , 1,406

Tan Chau, 1,774

Chau Thanh , 907

Tri Ton, 2,245

Phu Tan, 2,045

Chau Phu, 924

Tinh Bien, 2,428

Figure 1.2. Distribution of goat by district in An Giang, 2017

Source: Statistic yearbook of An Giang, 2018

Figure 1.2 shows the number of goats distributed across three geographic areas

in An Giang province. Goats are most concentrated in Tinh Bien, Tri Ton, the island of

Phu Tan and Tan Chau in 2017. The number goats increased because the price of goat

meat has been high in recent years: Price of goat meat (3.2 USD/kg LW) compared to

beef cattle (2.5 USD/kg LW) (Do Thi Thanh Van et al., 2018). It is one of the reasons

and potential to develop goat production in An Giang province and Vietnam also. But

goat production will be suitanable development, if it uses and improves by- products as

goat feed in this area efficiency.

- Goat raising purpose and farm scale.

In An Giang, goat raising began to develop in recent years (figure 1). The

number of goats is 13,950 heads in 2017 (Statistic yearbook of An Giang, 2018).

Nguyen Binh Truong (2016) showed that in An Giang province, goats were raised by

small scale and with three main purposes: selling meat product; breeding; breeding and

meat. Goat farming for breeding and meat accounted for the highest proportion of

74.4% of goats, followed by raising 18.9% with selling meat product and 6.67% for

selling breeding respectively. Normally, farmers usually choose the best goats based

on: good shape, healthy appearance from good mother to raise or sell the breed with

female and sell meat with male goat after 7-8 months old. On the other hand, goats

were raised by farmers spontaneously, the farmers learn how to breed each other, so

that the number of goats per farms average 6-10 heads accounted for 28.9% (26/90

surveyed households). A few households raise from 1 to 5 heads per household (12/90

surveyed households), number of goats from 11- 15 heads/farm was 26.7% (24/90

surveyed households, from 16-20 heads/farm with 14.4% (15/90 surveyed households)

and the number of households raising more than 20 heads accounts for 16.7% (15/90

farms) (Nguyen Binh Truong, 2016). According to the author, this result had called that

goat production is growing steadily.

- Goat management

Normally each household has a small cage for captive goats, with small area.

The cages are made near the house, surrounded by trees. Goat housing did not invest

too much money compared with raising pigs or cattle, goat farmers choose the trees

planted around the house to make 4-5cm square floor and wall paneling. Goat's cages

are made of simple materials such as bamboo, acassia aneura, coconut tree, etc. The

roofs are usually covered with leaves or tole. Therefore, 100% of the farmers make goat

cages, sheet metal roofs, convenient cleaning of effluent and leftovers of goats. Goat is

easy raising, less take care. They were raised by genetic traditional, therefore the

farmers did not use vaccine for goats.

With the advantages of low capital, easy to buy, to sell, goat raising is gradually

becoming a landlord for the poor farmers, who have limited land area or less productive

land. In the context of rising food prices, the output of some livestock is limited. The

goat raising is attracting many families to participate by utilizing agricultural

byproducts profitably. In Vietnam the domestic markets of goat products are good.

Although the marketing of goat products, and meat are limited, the local markets for

them are very good for the producers. There is a high demand for goat meat in many

different areas of Vietnam from the North to the South and the rate of increase in the

number of goats annually is not sufficient to meet the demand. Therefore, many

farmers and companies are preparing to build large commercial farms with the

importation of dairy goat breeds from developed countries for both milk and meat (Do

Thi Thanh Van and Nguyen Van Thu, 2018).

1.2.2. Feed and feeding management for goat

Feed is one of the determining factors of goat efficiency. Feed for goats is as

diverse as agricultural byproducts, leaves around the house such as banana leaves,

jackfruit, legumes, etc. Nguyen Binh Truong (2016) review said that, almost all goats

in An Giang province were fed natural grass with 33.31%, some large-scale farms (>=

20heads/farm) had grown elephant grass, VA06 grass, and Panicum mai-mum. Goat

feed is very diversified, abundant, they can utilize the variety of feed around the house.

Nguyen Huu Van (2012a) showed that banana stems and leaves are a source of good

feed for goats. When feeding goats banana leaves 100% in diet, DM consumption about

2.62% of body weight (DM basic) with digestibility of DM and CP were 62.0% and

59.1%. At that time goats ate 100% banana stems, DM consumption was 1.25% of

body weight (Nguyen Huu Van, 2012b). According to the author, the use of banana

leaves in combination with other foods as a source of food for goats would be better.

Many researchers reported that, leaves of trees which can grow around house

are good feed for goats. Both Paper Mulberry and Muntingia were feed source for

goats. Silivong et al. (2012) showed that the foliage of Paper Mulberry and Muntingia

represented 60-70% of the total DM intake, total DM intake of Paper Mulberry and

Muntingia were 31.3 g/kg LW and 30.8 g/kgLW, and coefficients of apparent

digestibility of OM and crude protein of goats fed Paper mulberry and Muntingia were

high but were not affected by NPN source. Even wild trees were a feed source for

goats, for example growth rates of goats on a sole diet of Mimosa foliage were 81 g/day

in confinement and 98 g/day under free grazing (Thu Hong et al., 2008).

Cassava leaves and cassava foliage were also excellent protein supplement

sources in the rations of ruminants. So many researches about ration of cassava leaves

or cassava foliage will be supplement for goat, increasing DM intake, digestibly of

crude protein and organic matter. There were many results: There was a 21% increase

in N retention when cassava was the main foliage (Phonethep et al., 2016). The use of

cassava peels, leaves improved the performance of goat (Onwuka, 2015).

Supplementing fresh, wilted or sun-dried foliage from cassava in the diet did not result

in any significant differences with respect to DM intake in percent of BW (3.4 to 3.6%)

and LWG of the lambs was ranged from 73 to 77g/day (Hue et al., 2010). The main

problems of fresh cassava leaves are high HCN contents (333 mg/ kg DM). The HCN

content in fresh cassava foliage reported by different researchers. According to Khang

and Wiktorsson (2006), Promkot et al. (2007) and Phengvichith and Ledin (2007), the

HCN content in fresh cassava foliage was 983, 1179 and 325 mg/kg, respectively,

while only 225 mg/kg was recorded in the experiment of Thang et al. (2010).

Therefore, when using fresh cassava foliage or cassava leaves as goat feed, they should

be reduced HCN content by processing. This is also a worry of the farmers in An

Giang, because they did not know to use cassava as feed for ruminants, they are afraid

of ruminants poisoning. Therefore, cassava in An Giang is wasted or burned in the

field, polluting the water and environmental pollution. An Giang is province in Mekong

delta, so it is affected by flooding every year. There is flooding from August to

November, and this cause a lack of natural grass, and agricultural by product for goat.

Figure 1.3. Farmers buy grass from another region

At that time, the farmers have to buy grass or agricultural by product for goat

from another region. According to Nguyen Thanh Binh (2018), agricultural byproducts

abounded in the Mekong Delta (including An Giang), but they were used for cattle, and

buffaloes while goats are modest and mainly in fresh form, not processed to form a

source of feed reserves with higher nutritive value. If the farmers implement

processing, then storage methods will contribute to solve the shortage of raw feed for

ruminants in the rainy and flooding season.

Goats are small ruminants usually raised in An Giang in three ways: intensive,

semi-intensive (semi-free), and extensive systems (grazing). In the intensive systems,

goats are kept in confinement and the feed is supplied entirely from outside. This system

is suitable where planted grasses and other supplements are available with 66.7% (60/90

surveyed households). In the semi-intensive systems, goats are grazed from 4-8

hours/day depending on the season, and additional feeds are supplemented at night with

32.2% (29/90) of surveyed households. This system is found suitable to the existing goat

farms in Vietnam. In the extensive systems, goats are grazed on available pasture without

supplementation. This system is common in mountainous and forest areas for the meat

goats, but low productivity, capital investment in breeding, breeding facilities, feed,

veterinary medicine, and public care. It is difficult to manage breeding and insemination

among the animals in the herd, environmental pollution caused by faeces, or not fully

utilized with 1.11% (1/90 surveyed households) in An Giang (Nguyen Binh Truong,

2016). Because goats are active, agile, have an unusual temperament and are hyperactive.

Goats are browsers and so are always looking for new food. They move very fast when

eating around the tree and eat only the most delicious food, then quickly move to the next

tree and dust. They like to eat at a height of 0.2-1.2m, they can stand on two feet to eat

the leaves, and even climb the tree to choose the delicious parts of the tree for eating, this

is problem when grazing in the limited grazing area.

1.3. OPPORTUNITIES AND CHALLENGE FOR GOAT PRODUCTION

Decision No. 929 / QD-UBND, 2015 and 2605/QĐ-UBND 2016 reported that

An Giang is a main source of agricultural products. Livestock development is one of

the development strategies of the province and should be considered by the

Government and investors. Since 2015, An Giang People's Committee has many

policies and strategies to support farmers development of livestock such as policies to

support agricultural restructuring (including livestock); support for breeding animals,

training for technical breeding, and improving nutritive value feed resources.

Construction of feed raw material areas: Strive to create quality feed equivalent

to the area planted with grass of about 900 ha by 2020 in Tri Ton and Tinh Bien. Focus

on developing livestock production systems.

To develop the technology of processing agricultural by-products (total mix

ratio) with available local resources (broken rice, bran, corn etc)

To gradually shift small-scale farming to more intensive farms and from small

and medium enterprises in livestock. Strive to reach the total number of ruminants up to

200,000 heads by 2020, corresponding to the average growth rate of 10% per year for

the period 2015-2020.

To build and reorganize animal slaughtering systems in industrial districts in

association with animal husbandry areas, veterinary hygiene, food safety and

environmental treatment. Simultaneously build modern slaughter facilities associated

with export processing.

Research to create value-added products from the livestock industry similar to

cattle skin used in the footwear industry, livestock waste, faeces used to fertilize plants,

or for growing earthworm to improve nutrition of soils.

Building the brand of animal products in the province (beef, goat meat): to

organize and manage the livestock sector more effectively, create higher value

livestock and help diversification and promotion of trade in livestock products better.

Recently, farmers and the local and central government of Vietnam have paid

more attention to enhancing goat production such as producing the development

policies, standards of goat farms, technical trainings and incentives for establishment of

goat production cooperatives, larger intensive farms and extensive clubs, improved

markets. There have also been collaborations among the universities, companies and

local institutions to create chances of investments on technology, finance and human

resources for improving production and markets. The veterinary networks, vaccines of

common diseases, parasite preventions and effective medicines are available to protect

the goat herds from diseases. However, goats also produce CH4 and CO2 during their

life time, which contribute to climate change. Therefore, strategies for reducing green

house gas emission of goats by feeding, nutrition balance, supplementations, and

breeding, should be applied (Nguyen Van Thu and Nguyen Thi Kim Dong, 2015) for

improving the livelihoods of the poor producers along the sea shore, where the effects

of climate change are greatest.

2. THE DIGESTIVE SYSTEMS AND ENTERIC METHANE EMISSION

IN RUMINANTS

The digestive tract is not only important for nutrient digestion and absorption, but

it is the largest immunological organ in the body protecting against exogenous pathogens.

2.1. RUMEN FERMENTATION AND METHANE PRODUCTION

2.1.1. Rumen fermentation

Anaerobic microbes in the rumen of the ruminant are able to degrade the

complex fiber source to provide essential nutrients that are readily digested by the host

while this is completely restricted in non- ruminants (Owen and Basalan, 2016). In term

of biochemical metabolism, ruminant microbes secrete the enzyme that hydrolyses all

macromolecule such as polysacharide, protein, lipid and other compounds to monomers

that are then fermented to the intermediate substrate (VFA, ammonia, ATP). The main

purpose of rumen fermentation is to generate energy for maintenance and synthesis

processes of microbial polymers which leads to the synthesis of more microbial cells

which in turn increases available protein to the animal (Phuong, 2012).

Ruminant diets

Roughage Concentrates

Amylolytic bacteria (pH> 5.5)

Starch etc Celluloses etc

Propionate bacteria (pH>6.2)

8H 8H Methanogenic bacteria (pH>6.2)

Cellulolytic bacteria (pH>6.2) CO2 Lactic CO2

VFA CH4 CH4 VFA Propionate

Figure 1.4. Microbes needed for fermentation (Leek, 1993)

2.1.2. Volatile fatty acids pattern

Volatile fatty acids (VFA) are important products of rumen fermentation. The

VFA are not only the major source of energy to the ruminant animals but also influence

methane production in the rumen. The concentration of volatile fatty acid (VFA),

mainly acetate, but some propionate and butyrate and largely part was absorbed via

rumen wall as free form. When rumen microbes ferment soluble sugar, they produce

VFA and ATP that are considered energy sources and are re-utilized for maintenance

and growth of microbes. Acetate may enter mainly fatty synthesis via actyl-CoA

intermediate than ketone bodies because it must not pass through this stage of

metabolism, while partly buturate is converted to ketone bodies (acetoacetate, β-

hydroxybutyrate) in the liver, the excessive accumulation of ketone bodies results in

ketosis as a pathological condition of the ruminant. Propionic acid is reported to be

concerned as a precusor of glucose synthesis with 80% propionate blood transfered to

hepatic for gluconeogenesis by Van Soest (1982), Preston and Leng (1987) all of whom

reported that propionate may contribute 80-90% of the glucose synthesized in sheep on

roughage diets (Cridland, 1984). High roughage rations will contain a higher percentage

of acetic acid whereas high concentrate rations will result in slightly higher levels of

propionic acid. With by-product diet or dry pasture, poorly absorbed glucose thus

gluconeogenesis play the major role to provide glucose needed for ruminant, while some

starch escape fermentation in grain-based diets can be digested in the small intestine.

Acetate Butyrate

Acetyl – CoA Butyryl – CoA Fatty acids

Ketone bodies Oxalacetate Glucose

TCA Cycl e Succinyl-CoA 2CO2

Propionyl-CoA

Propionate

Figure 1.5. Metabolic pathways of VFA (Bergman, 1993)

2.1.3. Protein metabolism

The rumen microbes are likely to utilize non-protein nitrogen source (NPN)

such as urea to contribute to the ammonia pool in the rumen. Level of ammonium in

rumen caused by microbial output is likely to convert ammonia to protein for synthesis

to microbial polymer. If there is low ammona then there will be nitrogen shortage to

microbes leading to low fermentation rate. In contrast, excessive ammonia results in

ammonia toxicity for the animal. Therefore, to utilize effectively, the conversion of

ammonia to microbial protein requires the availability of ATP energy generated by the

fermentation of carbohydrates. In other words, it requires the balance between

carbohydrate and NPN in the diet. Arccording to Wattiaux (1991), approximately 60%

of the amino acids absorbed through the small intestine is from a bacterial protein, and

the remaining 40% is from ruminally un-degraded dietary protein. In addition, the

rumen can use effective sources of protein from by-product sources.

The term of by-pass protein in rumen fermentation is defined to be protein that

escapes the degradation of rumen microbes. Two important factors influencing the

amount of protein bypassing degradation in the rumen are the length of time spent in the

rumen and fermentation of the protein (Miller, 2012). Leng et al. (1981) indicated that

by-pass protein in the ruminant diet was postulated on stimulating feed intake,

influencing the efficiency of microbial cell yield and digestion in small intestine,

providing essential amino acids post ruminally which are used efficiently, and in addition

increasing the total energy intake. If protein is too soluble and the sole diet in rumen,

dietary protein can be lost due to a large part of essential amino acid is fermented by

microbes, and microbial protein would escape the rumen to lower digestion to

compensate protein needed of the animal, meanwhile, the by-pass protein can provide

essential amino acids that are not synthesized by animal tissues, via absorption from

digested feed.

It can be seen that un-degradable and degradable protein play an important role

in rumen function and animal efficiency. Although it has not been well defined the

desirable proportion of undegradable and dregradable protein in ruminant feeding, but

it is quite evident that the diet has to contain sufficient protein to productivity (Miller,

2012). There are many studies that discuss the most effective ratio of rumen degradable

protein and un-degradable protein (RDP: RUP). Wang et al. (2008) and Tacoma et al.

(2017) did not found a significant difference among ratios of RDP: RUP on milk yield,

milk composion, and dry matter intake, but reducing the ratio of RDP: RUP reduced N

excretion in urine and faeces lead to enhance the efficiency of N utilization. Savari et

al. (2018) suggested that an RDP: RUP ratio of 65:35 could be adequate for cows in

early lactation with an average milk production of 44 kg and a DMI of 25kg.

2.2. METHANE PRODUCTION

Methane gas is produced from fermentation by rumen microbes. Domesticated

ruminants represents a loss of 2–15% of the gross energy (GE) intake by methane

production (Holter and Young, 1992), therefore being one of most important factors

contributing to inefficiencies in ruminant production systems (Moss et al., 2000).

In the rumen, methanogens are a large and diverse group of Archaea. By isolation

method, it is classified as Methanobrevibacter ruminantium, Methanobrevibacter smithii,

Methanobrecibacter millerae, Methanobrevibacter olleyae, Methanobacterium

formicicum, Methanobacterium bryantii, Methanosarcina barkeri, Methanosarcina

mazai and Methanomicrobium mobile (Qiao et al., 2014). Overall, the methanogens can

be divided into two groups: H2/CO2 and acetate-consumers with different levels of

energy yielding (-130.7 kJ/mol substrate and -32.3 kJ/mol substrate respectively). The

distribution of methanogen is diverse, it is assumed that they are free-swimming in

fluid or attach to digested solid or attach to protozoa (Morgavi et al., 2010).

In many tropical developing countries, goat production for milk and meat for

human demands is a priority choice for adapting to climate change, and the abatement

of enteric greenhouse gases emissions should be considered. However, goats being

small ruminants, which emit around 5.0kg CH4/head/year (Nguyen Van Thu, 2018),

could create greenhouse gases that influence climate change. Afshar et al. (2015)

concluded that it is notable that, other than management related strategies, three

important strategies including nutritional, biotechnological and microbiological

strategies are required for controlling and decreasing methane emission. Carla et al.

(2016) showed that the replacement of cereal grain with fibrous by-products did not

increase methane emissions (57.0 L/goat per day, on average).

2.2.1. Pathway of methane production

The pathway of methanogenesis has yet to be fully defined due to the diverse

microbes in the rumen create overall synergistic and antagonistic interactions.

However, it is known that formate, carbon dioxide, methanol, and acetate derived from

carbohydrate fermentation are concerned as terminal electron receptor for hydrogen to

form methane (Diagram 1). Based on biochemistry pathway, it can be seen that hexose

metabolism via the Emden-Meyerhof-Parnas pathway (EMP) produces pyruvate as an

intermediate associated with co-factor NADH generation (Leng, 2011). In the rumen,

methane production from CO2 substrate as an electron acceptor is a predominant

pathway of hydrogenotrophic methanogen. This bacterium group also uses formate as

an important electron donor and it is estimated to produce up to 18% of the methane

produced in the rumen. Many of the syntrophs are able to produce both H2 and formate,

and most of the methanogenic partners are able to oxidise both substrates to methane

(Leng, 2014). Acetate as substrate produce methane through the aceticlastic pathway by

Methanosarcina group but in terms of energy order, the energy level of methane

production from acetate is very low, thus, Methanosarcina population is limited in the

rumen (Morgavi et al., 2010). Furthermore, acetate is absorbed largely into the

bloodstream, thus, to the hydrogen would be contributed mainly by CO2

methanogenesis (Galand et al., 2005)

Figure 1.6. The reaction of methane generation

The process of methane production is a requirement in low partial pressure

hydrogen, which is necessary for the continuous fermentation in the rumen (Figure

1.6). However, the inhibition of methanogenesis would redirect the available hydrogen

into alternative energy-yielding metabolic pathways which are expected to improve the

productivity of ruminant but not adversely affect ruminal metabolism. Martinez-

Fernandez et al. (2016) had a comprehensive assessment on methanogenesis inhibition

by adding different levels of chloroform on steers fed roughage hay versus hay:

concentrate, the result showed that increasing chloroform level would increase the

expeulsion of hydrogen but there was no effect on both dry matter intake and fiber

degradation. The critical issue found in this study is that expelled H2 per mole of

decreased methane was lower on steer fed roughage hay only diet compared with hay

concentrate. The evaluation of rumen microbial response in this study showed that

decreasing Archaea and Synergistetes for both diets accompanied with increasing

Bacteroidetes (the bacteria involved in propionate production) but did not change

fibrolytic bacteria, fungi, and protozoa. These results can conclude that hydrogen was

redirected into products other than into CH4 and H2, probably in microbial protein, it

can be expected to improve the performance of the animal. Furthermore, using

roughage hay in the diet is the suggestion in slowing fermentation that creates a

condition for microbes utilizing H2 more effectively as a reduction of methane

production, meanwhile, highly concentrates fermentation in diet would high partial

pressure of H2.

2.2.2. Manipulation in mitigation of methane production

Nutritional mitigation of CH4 production is founded on 3 basic approaches:

(1) VFA production patterns will be altered by feed ingredient.

(2) Increased rate of passage, which can alter microbial populations and VFA

production patterns and shift some digestion to the intestines;

(3) Choosing better quality diets to increase production will reduce the CH4 associated

with maintenance energy requirements.

Most microorganisms in the rumen and lower digestive tract use fermentation to

fuel their cellular function and produce Short-Chain Fatty Acids (SCFAs) as a

byproduct. The SCFAs, namely acetate, propionate, and butyrate, are subsequently

absorbed through the rumen wall and metabolized by the host (Van Soest, 1994)

Now, many researchers have focused on factors (1) and (2) above, for reducing

CH4 emissions from ruminants. Feed ingredients provide the substrates for microbial

fermentation, and differences in feed digestibility and chemical composition alter the

amount of energy extracted by the microbes and the patterns of VFA and CH4

produced. The proportions of VFA affect the amount of CH4 produced, because

propionate formation consumes fewer equivalents, whereas acetate and butyrate

formation generate H2 for methanogenesis (Hungate, 1966). In this case, we also focus

to find the feed ingredients that can provide the substrates for microbial fermentation

such as biofilm, and can control the proportion of VFA, reduce CH4 produced.

Based on the mechanism of methane production, a series of studies in

replacement of urea by nitrate as electron acceptor to outcompete methanogen lead to

reduce methane production were conducted both in vivo and in vitro experiments (Trinh

Phuc Hao et al., 2009; Ngoc Huyen et al., 2010; Inthapanya et al., 2011; Binh Phuong

et al., 2011). In these studies, on ruminants, the animal was adapted to gradually

increase nitrate salt in the diet without methemoglobin.

De-fauna protozoa by oil is believed to affect the protozoa depletion population

where methanogen attachment. Although the mechanism of action is poorly

understood, it may be related to the lipophilic nature of compounds such as anethol

which facilitates permeation of essential oil across the protozoal membrane (Cardozo et

al., 2004). Saponin and tannin have also been reported as removing protozoa. The

effect of saponin seems to be mediated by their capacity to form irreversible complexes

with cholesterol in the protozoal cell membrane to cause the destruction of the cell

membrane, cell lysis and death (Francis et al., 2002). In the case of tannins, reported

results are somewhat confusing because some studies report unclear effects (Sliwinski

et al., 2002), while others report a clear defaunating effect (Bhatta et al., 2009;

Monforte-Briceno et al., 2005). Bhatta et al., 2009 stated that the combination of

hydrolyzable and condensed tannins exhibits higher antiprotozoal activity than

hydrolyzable tannins alone. Although the mode of action of tannins on protozoa is not

clear, it might be like that observed on bacteria.

Preston et al. (2013) assumed that there is a correlation between lower soluble

crude protein in fish meal with lower methane production when it is compared with

groundnut meal being higher solube CP and higher methane production. This author

interpreted that ammonia is likely to produce rapidly forms of highly soluble proteins

of diet, and soluble amino acids give rise to hydrogen sulphide, which is an effective

electron sink. It is thus possible that there might be some negative feedback of this

rapid production of ammonia from dietary protein on the pathway of ammonia

formation from hydrogen.

The recent studies have mainly been in vitro screening of good nutrients, agents

and feed sources to potentially reduce greenhouse gases such as essential oils, protein

sources, probiotics, TMR, silages, etc. After that the in vivo studies could be tested and

then implemented for applications (Do Thi Thanh Van et al., 2018). The value of CH4

production remarkably significantly decreased with increasing coconut oil

supplementation in the diets (Nguyen Thi Kim Dong & Nguyen Van Thu, 2018). This

result is consistent with the findings that CH4 production reduced in the diet

supplemented with 14% coconut oil versus without coconout oil supplement (12.6

versus 14.2 l/day) (Delgado et al., 2013). In an in vitro gas experiment adding

probiotics to the substrates Huynh Doan Nghich Luy (2016) found that there was a

significant reduction of CH4 and CO2 for the probiotic treatments. Probiotics including

lactic acid and Bacillus bacteria, Saccharomyces yeast which are useful for the animals,

particularly improve the nutrient utilization, growth and milk production of ruminants

(Dunne et al., 1999). Recently, Riddell et al (2010) stated that probiotics reduce

methane production, depress the growth of pathenogenic bacteria by reducing rumen

pH and growth competition to methanenogenic bacteria.

Biochar is known to increase the methane production in bio digesters but

mitigates methane production in the rumen, improves the growth biochar is included at

1% of DM basis in the diet of cattle (Leng et al., 2012a; Leng et al., 2012b). Leng et al.

(2012a,b) showed that incorporation of biochar, prepared by carbonization of rice husks

in a gasifier stove reduced methane production both in vitro and in vivo (Leng 2012c).

The action of biochar in the rumen resulted from it's potential to act as an improved

location for biofilm microbial consortia and that this would facilitate microbial activity,

including oxidation of methane by methanotrophic organisms. The idea that biochar

could act as a functional site for improved biofilm formation is based on the large

surface to weight ratio (>30m2/g and up to 500m2/g), creating opportunities for

adsorption of both micro-organisms, nutrients and gases.

Biocarbon pyrolyzed at high temperature in a manner that generates a very high

surface area is called engineered or activated biocarbon and has been theorized to

promote the formation of microbial biofilms in the rumen (Leng et al., 2012a, 2014), a

process essential for ruminal feed digestion (McAllister et al., 1994). Further, biochar

may lower the production of ruminal CH4 emissions both in vitro (Hansen et al.,

2012; Leng et al., 2012a,b) and in vivo (Leng et al., 2012c). It has been suggested that

biochar reduces ruminal enteric CH4 emissions by altering rumen microbial biofilms,

decreasing rumen methanogens and increasing rumen methanotrophs (Leng et al.,

2012a,b,c; Toth and Dou, 2016)

3. POTENTIAL OF CASSAVA FORAGE FOR GOAT PRODUCTION

3.1. PLANT AREA AND DISTRIBUTION OF CASSAVA AND YIELD OF

CASSAVA IN VIETNAM, AN GIANG

In Vietnam, cassava is a major source of income for farmers in areas of low

fertility soil and adverse climatic conditions. It is also a source of raw materials for

starch processing and for the animal feed industry with high commercial value. Cassava

has been planted throughout the 7 agro-ecological zones of the country: The Red River

Delta, the Northern Midlands and Mountains, the North Central Coast, South Central

Coast, Central Highlands, South East and Mekong Delta. However, the focus is mainly

in the Central Highlands (Figure 1.3)

According to the Ministry of Agriculture and Rural Development at the end of

November 2017, the area of cassava planting in the whole country was 1,400 hectares.

Cassava has previously been cultivated mainly for the roots. Small cassava stems can

be used for the next year’s growth. Normally, cassava foliage was thrown away in the

field. Based on the areas of cassava cultivation in 2017, the yield of cassava root was

20.5 tonnes/ha (Statistic yearbook of An Giang, 2018), the amount of foliage available

at root harvesting is equivalent to about 30% of the root yield and was an estimated

6.15 tonnes of dry matter per hectare (Erdmann et al., 1993). The amount of cassava

foliage produced was an estimated 8.6million tonnes per year in An Giang. This was a

large amount of cassava foliage, but they were used only slightly at the harvesting time,

but after 2 – 4 days harvesting, the leaves would fall down, and only stems remain.

They were thrown away, although this resource is very good feed for ruminants.

Figure 1.7. Plant area of cassava in Vietnam, 2017

Source: Ministry of Agriculture and Rural Development, 2017

About 70% of the cassava area of the country is grown using hybrid varieties;

The remaining 30% is local varieties. In the hybrid varieties, the KM94 variety is

dominant (73%), the rest is other varieties (Nguyen Huu Hy et al., 2014). The popular

cassava varieties were: Xanh Vĩnh Phú; Gòn; Nếp; Ba Trăng; Lá tre; Mì kè; HL23;

KM94. KM140, KM98-5; KM95-3, KM98-1, KM 98-7. KM111-1; CM 101; SM937-

26; KM419, NA1, KM21-12, 08SA06. There are two kinds of cassava: Sweet and bitter

cassava. Sweet cassavas are used as food consumption for human; bitter cassavas are

used for industrial processing such as wheat flours, animal feed, etc. In An Giang there

were two kinds of cassava variety (Sweet cassava or Mi ke and bitter cassava).

Ubi et al. (2008) found that the total HCN content of the roots was not correlated

with the content in the leaves of the same plant. Therefore, the classifications of “bitter”

and “sweet” may not be applicable when regarding the whole plant. So, based on the

content of HCN in cassava roots, it is divided into two groups of cassava varieties: sweet cassava and bitter cassava. Sweet cassava contains about 20 - 30mg kg-1 of fresh roots; bitter cassava contains 60 - 150 mg kg-1 of fresh roots (Mai Thach Hoanh, 2004). The

sweet cassava is local breeds, low yield, small roots, fresh and cassava roots are used for

human food. The bitter cassava is popular and grown with large area, high production.

They are grown with large area in high land, and South-Central Coast. Cassava roots are

used to produce flour, processing starch, and industry products.

"Sweet" or low- cyanogenic potential (CNP) cassava (root CNP less than 50 mg kg-1 as HCN fresh weight basis) is generally considered safe for consumption with only

basic processing (e.g., peeling and cooking), whereas "bitter" or high-CNP cassava (root CNP greater than 100 mg kg-1 as HCN fresh weight basis) must be processed

prior to consumption to eliminate the cyanogens or reduce them to physiologically

tolerable levels (Cooke 1983; Dufour 1988a). Other reports show cyanogenic glicosides

concentration in the roots. Sweet cassava has HCN concentrations below 100 mg

HCN kg–1 and bitter cassava show concentrations above 100 mg kg–1 HCN (McKey

et al., 2010). Cassava plants are generally categorised as bitter or sweet, depending

upon their cyanide content. The low HCN, or sweet cassava, has less than 50 ppm of

cyanogenic equivalents, while the high-HCN, or bitter cassava has more than 100

ppm (Wilson and Dufour, 2002). The major difference between low- and high-CNP

cultivars is limited to the CNP of the root parenchyma. The CNP of the root periderm

(peel, cortex) and aerial portions of the plant are high in both low- and high-CNP

cassava (McMahon et al., 1995).

3.2. POTENTIAL OF CASSAVA FORAGE FOR GOAT PRODUCTION

3.2.1. Proportion yield of parts of cassava forage

The yield of cassava forage and differences in DM foliage yield could be due to

the differences in variety (Gomez and Valdivieso, 1984; Simwambana et al., 1992),

fertilizer (Molina and ElSharkawy, 1995), age at first cutting and interval between

cuttings (Lockard et al., 1985; Simwambana et al., 1992; Tung et al., 2001; Hong et al.,

2003). Although there is no data shown from the present study on the effects of seasons

on cassava forage yield, DM yield was reduced in all the treatments during the last

three months of the experimental period, most likely due to the onset of dry season.

3.2.2. Composition of cassava forage, parts of cassava forage

The chemical composition of cassava forage depends on many factors including

variety, harvesting interval (Khang et al., 2005), difference fertility of soil, processing,

and also climate, environmental conditions, such as drought (leading to an increase in

cyanogenic potential), geographic location age of the plant by Garcia and Dale (1999)

and soil nutrient supply as reviewed in Burns et al. (2013).

Table 1.1. The chemical composition of cassava forage variety

Cassava

Tannin

HCN

DM%

CP %

NDF (%)

Sources

proportion

(%)

mg/kgDM

Cassava Root

26.0

1.0 - 3.0

Stupat et al. (2006)

Cassava Leaves

18.6 - 20.7 20.7 - 28.5 2.86 - 4.36 489 -730 Hue et al. (2012)

Cassava Leaves

26.0

23.9-34.7

Phuc (2000)

Cassava Foliage

24.0

Buitrago (2010)

(leaves + petiole)

Cassava Foliage

32.7

17.6

47.9

Cassava Stems

54.1 33.4

5.5

Thanh et al. (2013)

Cassava Hay

85.6

16.5

52.9

Cassava Stems

33.7 ± 0.69 5.7 ± 0.06 60.3± 0.49

108.6 ±1.12 Lam (2013)

Dried cassava top

87.2

17.1

42.6

2.13

Khang et al. (2016)

3.2.3. Using cassava foliage for goat production

Many studies have focused on cassava foliage as a feed for animals, especially

for ruminants. Fresh cassava foliage, cassava leaves, cassava hay; cassava foliage silage

has been fed to cattle, with good results (Thang et al., 2010; Wanapat, 2009, Truong

Van Hieu et al., 2014).

According to Sath et al. (2008), increasing the level of sun-dried cassava foliage

supplementation improved total DM and N intake of cattle fed a basal diet of rice straw

and para grass. Maximum weight gain and N retention were achieved when 40% of

total N intake (1.3 g CP/kg BW) came from cassava foliage, corresponding to about 0.7

kg DM/100 kg BW, while higher cassava intake did not further improve animal

performance. Cassava foliage is also a good protein source for small ruminants.

Feeding cassava foliage (wilted, sun-dried or ensiled) to goats housed at night after

day-time grazing increased growth rates and reduced nematode parasite egg counts

(Phengvichith et al., 2011).

Previous studies showed that feeding cassava foliage hay to penned goats

resulted in improved growth performance (Ngo Tien Dung et al., 2005; Phengvichith et

al., 2006). An additional benefit from feeding cassava foliage to goats is that the

tannins appear to modify or control nematode infestations (Seng Sokerya et al., 2003).

Fresh or sun-dried cassava foliage is a valuable supplement for goats receiving low or

medium quality diets (Kounnavongsa et al., 2010).

3.2.4. Antinutritional factors (Tannin and HCN) of cassava forage

Besides the high protein content found in cassava forage, it also has a

component that significantly affects the digestion of food and the metabolism of rumen

nutrients that is tannin and HCN. These two substances will affect the ability to eat, and

digestibility for animals, especially ruminants. According to Sousa et al. (2003), sheep

and goats are considered to be highly susceptible to HCN toxification, and the tolerance

level of sheep was 2.0 to 4.0mg HCN/kgBW (Conn, 1979; Kumar, 1992). Aslani et al.

(2004) gave doses corresponding to 5.8 and 10mg HCN/kg. So, cassava leaves’ use as

goat feed is limited.

Cassava plant is a sources of protein and good energy for livestock feed, but

using fresh cassava forage as a feed for ruminants can be a problem due to its fairly

high content of hydrogen cyanide (Hue et al., 2010). According to Ravindran (1993),

the normal range of HCN content in cassava foliage is 200 to 800 mg/kg of fresh

leaves, with the variation being attributed to genetic, physiological and edaphic factors,

and climate. One of the more important differences between different varieties of

cassava is in the content of HCN. The cyanide levels in cassava depend on the variety

and age of the plant, the soil conditions, presence of fertilizer and weather, among other

factors (Ngiki et al., 2014).

In many cases the varieties with high HCN content are referred to as very bitter

or bitter varieties while those low in HCN are classified as sweet varieties (Mlingi et

al., 1995). HCN content in leaves was higher than in petioles or stems and the content

in leaves varied less in soils than in varieties (Arvidsson et al., 2003). There were

considerable differences in chemical composition of the foliage from different varieties

harvested at different harvest occasions, harvest interval.

The cyanide concentration of root parenchyma was less variable than that of

leaves and root peel; It showed a higher cyanide content in the parenchyma (900 to

1000 mg/kg DM) than the other three cultivars, which ranged from 100 to 200 mg/kg

DM. The local cultivar was the only one in which the cyanide content of leaves was

higher than that of the root peel (Gómez et al., 1985); the HCN content in cassava

foliage was much lower in the local variety and it also declined with foliage maturity.

According to Hue et al. (2012) the content of total tannins in cassava foliage

increased with increasing leaf maturity at the harvest but no differences were obtained

between varieties. Another important aspect of cassava foliage is the content of

condensed tannins. Khang et al. (2005) reported that unlike HCN, the content of

condensed tannins in foliage increased at longer harvest intervals, ranging from

approximately 3.5% of DM at 45 days harvest interval to around 4.3% of DM at root

harvest stage. Significant tannin differences in varieties was also reported by Oni et al.

(2011). The impact of condensed tannins in cassava forage on protein digestibility was

studied by Reed et al., 1982 but information addressing cassava harvested for forage is

still limited. The levels of the anti-nutrients (cyanide, phytate, oxalate and tannin) was

significantly reduced by processing of cassava roots such as cooking, fermentation and

soaking, and hence render the processed roots safe for human consumption, animals.

(John Manano et al., 2017).

The tannins are traditionally broadly divided into two categories: hydrolysable

tannins (HTs) or condensed tannins (CTs) on the basis of their structure; Hydrolysable

tannins have a central carbohydrate core the hydroxyl groups of which are esterified to

various phenolic carboxylic acids. This group of tannins is easily hydrolyzed to give

glucose or a polyhydroxy alcohol and the various phenolic acids. The way in which

tannins affect animal performance is not exactly clear. Tannins form complexes with

proteins and carbohydrates in the feeds, and with digestive enzymes. As a results

nutrient digestibility is depressed. Other effects of tannins include reduced feed intake,

increased damage to the gut wall, toxicity of absorbed tannins and reduced absorption

of some minerals. These effects can largely be attributed to condensed tannins.

Condensed tannins reduce protein degradation in the rumen and increase the flow of

amino acids to the intestine for absorption (Waghorn et al., 1994).

3.2.5. Reducing methods antinutrients factor in cassava foliage

The tannin and HCN contents of cassava depend on the variety, harvesting

interval, proportion of cassava, and processing method (Table 1.2).

Table 1.2. Tannin and HCN content of cassava foliage

Cassava foliage

Variety

Fresh Wilt Dried Silage

Sources

Tannin %DM

2.87

2.83

KM94

Man et al. (2002)

HCN mg/100g

28.19

23.58

HCN mg/kgDM

Sweet cassava

273

107

Chhay Ty et al. (2007)

HCN mg/kgDM

Bitter cassava

338

134

Tannin g/kgDM

KM 94

Hue et al. (2010)

HCN mg/kgDM

333

217

Tannin %

4.21

KM 94

Khang et al. (2005)

HCN mg/100gDM

28.6

Many researchers reported that the HCN content in cassava is reduced by

processing. Padmaja (1989, 1995), Phuc et al., (2000); Cardoso et al. (2005), Man and

Wiktorsson (2001, 2002) and Borin et al. (2005) have investigated the effect of

different processing methods on the chemical contents and the nutritional value of

cassava leaves and roots.

Drying is the most popular practice used to reduce cyanide content of cassava.

Sun drying is more effective at eradicating cyanide than oven-drying because with this

method the cyanide is in contact with linamarase for a longer period (Ngiki et al.,

2014). Ravindran (1991) stated that sun-drying alone can eliminate almost 90% of

initial cyanide content. Tewe and Iyayi (1989) compared the HCN level in fresh, oven-

dried and sun-dried cassava. The HCN levels in the root, pulp and peel were a

maximum of approximately 416, 200 and 815 mg/kg respectively in the fresh samples,

64, 31 and 1,250 mg/kg in the oven-dried samples and 42, 27 and 322 mg/kg in the

sun-dried samples. Ravindran et al. (1987) found that fresh cassava leaves had an

average HCN content of 1,436 mg/kg, but when they were sun-dried this was reduced

to 173 mg/kg. Additionally, Khajarern et al. (1982) found HCN content was reduced

from 111.83 to 22.97 mg/kg when cassava roots were sun-dried for 6 days. Gomez et

al. (1984) found that more than 86% of HCN in cassava 1984 was lost by sun-drying

due to evaporation of free cyanide at 28 °C.

Furthermore, cassava hay contains only 2-4% condensed tannins as compared to

more than 6% in mature cassava leaves at time of root harvest. Producing cassava hay

as a high-protein fodder is a means of increasing the protein to energy ratio of the

whole cassava crop (Wanapat, 2001).

Fermentation also reduces the cyanide content of cassava products. Fresh

cassava root contains approximately 400 to 440 mg/kg HCN which can be reduced to

84 mg/kg by wet fermentation and 14 mg/kg by solid-state fermentation (Muzanila et

al., 2000), and to 15 or 8 g/kg when turned into unfermented or fermented meal,

respectively (Udedibie et al. 2004). Soaking of cassava roots preceding cooking and

fermentation can enable heightened extraction of soluble cyanide by removing

approximately 20% of free cyanide in the fresh root after 4 h (Tewe, 1991). Boiling

cassava chips also removes some of the cyanide; approximately 90% of free cyanide is

removed within 15 min of boiling and 55% of the bound cyanide is removed after 25

min of boiling (Cooke and Maduagwu, 1985). Okoli et al. (2012) found that there is

great variation in the physiochemical and HCN contents of cassava processed by

different methods. Samples that had been peeled, fermented and sun-dried had higher

water holding capacity and digestible fibre compared with samples not exposed to these

methods, and samples that has been oven toasted prior to milling had higher crude fibre

and HCN values compared with samples that were not toasted (100 – 200 mg/kg

compared with 5 – 15 mg/kg). In conclusion, there is not one optimum method for

processing cassava, but rather a combination of different techniques is required based

on the specific variety of the cassava.

Ensiling also reduced the HCN content of cassava products. Ensiling is one

among several techniques recommended for practical conditions to preserve the quality

of feed materials during periods of excess (McDonald et al., 1991). An advantage of

this method is that plant materials can be preserved at any time of the year, even when

weather conditions are not suitable for sun-drying. The ensiling process ensures not

only increased shelf life and microbiological safety, but it also makes most food

resources more digestible (Caplice and Fitzgerald, 1999). It has also been shown that

fermentation of cassava leaf and foliage reduces toxicity levels of HCN (Chhay et al.,

2001; Sokerya et al., 2009).

According to Dang Hoang Lam (2013), HCN content of cassava stems was

strong reduced by treated with urea or molassic silage. HCN content of cassava stems

treated with urea was lower than HCN content of cassava stems silage. Specially,

cassava stems treated with 2.5% urea after, HCN content was not detected

On the other hand, using brewer’s grain from the small amounts is as a

“prebiotic” in reducing the sub-clinical toxicity caused by the cyanogenic glucosides in

the cassava foliage. According to Phuong et al. (2016) reported that major benefits in

growth of cattle (from zero to 600g/day) when brewers’ grains (at only 4% of the diet

DM) were added to a similar diet of cassava pulp-urea-cassava foliage (bitter variety).

It was also observed that urinary excretion of thiocyanate was substantially reduced by

supplementation with the brewers’ grains. These authors concluded that the benefits

from the small amounts of brewers’ grains (4% of diet DM) possibly were due to a

“prebiotic” effect of this supplement in reducing the sub-clinical toxicity caused by the

cyanogenic glucosides in the cassava foliage.

4. IMPROVING GOAT PRODUCTION AND REDUCTION OF

METHANE EMISSION PRODUCTION

4.1. IMPROVING STRATEGY GOAT PRODUCTION

Livestock development in An Giang is an urgent and practical issue, especially

goat raising, as goat production is one of the solutions that can help farmers increase their

incomes and solve the problem of jobless farmers, and less land for production. The

natural conditions are erratic in this area, agricultural byproducts are over-harvested but

there are shortages in dry season or flood in rainy season. Because the livestock farmers

are small scale and employ traditional raising systems, they do not know how to stockpile

or produce agricultural byproducts immediately after harvesting to ensure that feed is

available throughout the year. This problem was interesting for the An Giang province

Government, and they developed policies for farmers such as training for technology to

improve nutritive value of agricultural by products, and processing.

4.2. CLIMATE CHANGE AND REDUCTION OF METHANE EMISSION

PRODUCTION

In recent years Vietnam has suffered the negative effects of climate change

including droughts, strong storms, flooding, and slash lands, which have caused lost of

agricultural production and affected human livelihoods. Do Thi Thanh Van (2006)

reported that goats’ thriving in harsh tropical environments represents a climax in the

domestic ruminant’s capacity to adjust to such areas, where water sources are scarcely

distributed, and feed sources limited in quantity and quality. The ecological,

physiological and feed adaptive behavior of goats in the unfavorable tropics makes them

an appropriate candidate to sustain livestock production in the context of climate change.

Greenhouse gases are the main reasons causing this phenomenon. To adapt to

the climate change, goats as the ruminant, its production needs to mitigate the CH4 and

CO2 in the management, therefore number of studies aimed to abate the enteric

greenhouse gases emissions without reducing the production yields has been done. The

recent studies have mainly been in vitro screening of good nutrients, agents and feed

sources to potentially reduce greenhouse gases such as essential oils, protein sources,

probiotics, TMR, silages, etc. After that the in vivo studies could be tested and

successful ones could be implemented.

There are many studies that have been conducted with hypothesis reducing

methane production.

The reduction in methane emissions was calculated on the basis that carbon dioxide

production reflects energy utilization by the animal, so the ratio of methane to carbon

dioxide in eructed gas is a measure of the relative production of methane as a function of

the intake of metabolizable energy (Madsen et al., 2010; Leng and Preston, 2010).

Kongvongxay et al. (2011) investigated the effects of four different levels of a

tannin-rich foliage (Mimosa pigra) on feed intake, digestibility, nitrogen retention and

methane production in four goats fed a basal diet of Muntingia calabura. Each goat was

provided with each of the diets for a period of 10 days. Rumen fluid, urine and faeces

were chemically analyzed to monitor the effects of the diet, and each goat was placed

inside a sealed chamber (made with a bamboo frame and plastic sheeting) after the

second and fourth feeding period to measure the methane: carbon dioxide ratio of

eructed gas. The results showed the greatest methane reduction (42%) with 72% of the

dietary N from mimosa.

Sophea and Preston (2011) investigated the effects of different levels of

supplementary potassium nitrate replacing urea on the growth rates and methane

production in goats fed rice straw, mimosa foliage and water spinach. It was postulated

that nitrate could replace carbon dioxide as an electron acceptor in the rumen with the

generation of ammonia instead of methane. In this reaction, nitrate is reduced to nitrite

and then to ammonia, resulting in lower methane gas emission. Therefore, it was

hypothesized that a nitrate salt could potentially replace urea as a source of non–protein

nitrogen (NPN) because, as with urea, it would provide a fermentable nitrogen source

for microbial protein synthesis.

Leng et al. (2012) explored the hypothesis that there will be an additive effect

on reduction of methane emissions from adding both biochar (increasing the potential

microbial habit) and nitrate to the diet of cattle fed a basal diet of fresh cassava root

chips supplemented with fresh cassava leaves. Twelve young local “Yellow” cattle

undertook a trial that lasted 98 days following a 21 days period of adaptation to the

diets. At the end of the experiment, a sample of mixed eructated and respired gas from

each animal was analyzed for methane and carbon dioxide using the Gasmet equipment

based on the approach suggested by Madsen et al. (2010). Live weight gain was

increased 25% by adding biochar to the diet and tended to be decreased when nitrate

replaced urea. Feed conversion was improved by biochar and by urea replacing nitrate.

Feed intake was not affected by supplementation with biochar nor by the NPN source.

Both biochar and nitrate reduced methane production by 22% and 29%, respectively;

the effects being additive (41% reduction) for the combination of biochar and nitrate.

The availability of brewers’ grains is limited to locations close to beer

factories, Keopaseuth et al. (2017) therefore investigated the use of Cassava foliage;

replacing brewer’s grains as a protein supplement for twelve Yellow cattle fed cassava

pulp-urea and rice straw. The maximum growth rate was recorded when the brewers’

grains provided 9-17% of dietary dry matter, and the ratio of methane to carbon dioxide

in mixed eructed gas and air declined dramatically with a curvilinear trend as the fresh

cassava foliage replaced brewers’ grains in the diet.

Recently, farmers and the central government of Vietnam have paid more

attention to enhancing goat production such as producing the development policies,

standards of goat farms, technical trainings and incentives for establishment of dairy

goat production cooperatives, lager intensive farms and extensive clubs, improved

markets, etc. There have alsobeen collaborations among the universities, companies

and local institutions to create chances of investments on technology, finance and

human resources for improving the production and markets. The veterinary networks,

vaccines of common diseases, parasite preventions and effective medicines are

available to protect the goat herds from diseases. However, goats also produce CH4 and

CO2 during their life time, which contribute to climate change. Therefore, strategies of

reducing green house gas emission of goats by feeding, nutrition balance,

supplementations, and breeding. should be applied (Nguyen Van Thu and Nguyen Thi

Kim Dong, 2015) for improving the livelihoods of the poor producers along the sea

shore, hill land, central highland. which are affected by climate change (Do Thi Thanh

Van, 2018). Especially in An Giang, there are many developing policies such as

Decision No. 929 / QD-UBND, 2015 and 2605/QĐ-UBND 2016 that declare An Giang

is relies on agricultural products, Livestock development is one of the development

strategies of the province and should be considered by the Government and investors.

In recent years, from 2015, An Giang People's Committee has many policies and

strategies to support farmers development of livestock such as policies to support

agricultural restructuring (including livestock); support for breeding animals, training

for technical breeding, and improving nutritive value feed resources.

5. CONCLUSIONS

Cassava is a high yield in An Giang, Vietnam. Cassava is not only a food crop,

but also an industrial crop that produces alcohol, sugar, monosodium glutamate, starch

for processing. In addition, the main products of cassava processing produce a large

amount of by-product for livestock feed. Although their nutritional value is not high,

they also have positive effects on livestock. On the other hand, there were strengths for

growing cassava including improving high production of cassava varieties and more

industrial factories. There are also weaknesses and threats: climate change, soil erosion,

strong storms, and hot weather. So that the current reality suggests that the issue of

supplementary research, how to supplement and develop appropriate processing

methods to improve the utilization and improvement of the nutritional value of the

byproduct use in livestock production still needs to continue to be researched to

maximize the digestibility of ruminants and agricultural by-products in our country

nowaday. In light of the achievements already made and the future risks of climate

change, the aims of this study are to improve utilization of cassava forage effeciency

for sustainable goat feeding to increase performance and reduce enteric methane

emission from goats in An Giang province, Vietnam.

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CHAPTER 2 EVALUATION OF THE POTENTIAL OF CASSAVA

FORAGE AS FEED FOR GOATS IN AN GIANG

PROVINCE, VIETNAM

Abstract

The aim of survey was to evaluate cassava forage and goat production before

their potential in developing ruminant production in An Giang. A baseline survey was

conducted to investigate the current status of cassava and goat production in An Giang

Province. Data were collected from Statistic office of An Giang and household

interviews on 60 households raising goats amd 60 households growing cassava in Tinh

Bien and Tri Ton districts. Results showed the number of goats increasing in recent

years. However, goat production systems were still extensive, exploiting natural feed

resources with small herds of indigenous goats, which have small sizes and low growth

rates. Besides, planted area of cassava was increased. The dry matter of cassava forage

(cassava livestock feed) was averaged 5 tons/ha, and that is a feed resource for

ruminants in flooding or rainy seasons. But the farmers did not use cassava forage as

feed for ruminants, specially goats, although this by-product is a good protein sources

for animals.

Key words: Goats production, cassava forage, green matter, dry matter

1. INTRODUCTION

An Giang is a watershed province in the Mekong Delta, which is one of the

largest cultivated areas in the Mekong Delta. The total area of agricultural land is more

than 282,676 ha, of which paddy land accounts for more than 85.2% (Statistic yearbook

of An Giang, 2018). An Giang is one of the two provinces in the Mekong Delta with

hills and mountains, mostly in the northwest of the province, in Tinh Bien and Tri Ton

districts. An Giang is in the tropical monsoon climate, with two distinct seasons: rainy

season and dry season. The annual average temperature is about 200C - 360C, the

average annual rainfall is about 1400 - 1500 mm. The rainy season is the least in

February and the rainy season is the highest in September. The average humidity is 75-

80%. The basic climate is favorable for agricultural development. Due to the

topography, the land resources are divided into different types: alluvial soil, alkaline

soil, mountainous land. Hilly land is mainly distributed in two districts of Tri Ton and

Tinh Bien, a small part of Thoai Son district (Ba The area). Total area of hilly land in

An Giang is about 29,320 ha, accounting for 8.6% of total land area of the province.

So, the area of grazing land is limited, the grassland is also limited. The cassava was

planted in there, it is not so much (representing 0.5% of agricultural land). The

production of cassava roots in this area was 28.7 ton/year. It is estimated that an

amount of cassava foliage is produced 61 thousand tonnes. The reason is difficulties in

drying the straw or other roughage in the rainy season, but by- production is an

underutilized resource for feeding livestock. The purpose of planting cassava in this

area is to harvest roots, cassava foliage is underutilized, being left to rot in the monsoon

season (flooding season) and burned in the dry season. Even with a small number of

cattle in the province by 98,758 heads in 2017 (Statistic yearbook of An Giang, 2018) a

sufficient supply of roughage is not easy to find during the rainy season, and cassava

foliage is an underutilized resource for feeding livestock, especially in the hilly land

area. These areas are suitable for goats raising. The design of this thesis responds to

tendencies that have been observed in the development of crop and livestock systems in

Tinh Bien and Tri Ton districts in An Giang province. The survey described in showed

that there is an increasing tendency to plant cassava both as a food crop and as a source

of starch for industrial processing. At the same time there are major trends in ruminant

livestock numbers, with the population of goats increasing.

2. MATERIALS AND METHODS

The survey was conducted in An Giang province, based on secondary data of

An Giang Statistical Office's, 2017, two districts were chosen: Tri Ton and Tinh Bien.

They represented two ecoregions in An Giang. Tri Ton district is low land and Tinh

Bien is high land. Sixty households in each district that were planting cassava or raising

goats, and both were randomly chosen for interviewing.

2.1. THE FOLLOWING INDICATORS WERE USED IN THE INVESTIGATION

OF THE SURVEY

From secondary data:

- Planting area and cassava productivity in each district in the An Giang province

- Number of goats raised in each district in the An Giang province

The following indicators were used to select 120 households (60 households

have grown cassava; 60 households have raised goats).

In the cassava growing households, we focused on: Cassava varieties, Cassava

productivity, purpose of planting, cassava forage after root harvesting, yield of fresh

and dry cassava forage and output.

In term of targets in goat households we measured: number, breed & breeding,

feed & feeding, goal of goat rasing, market and systems. In this case, goat production

was divided into three groups: Intensive, semi- intensive and extensive systems. In the

intensive systems, goats are kept in confinement and the feed is supplied entirely from

outside. In the semi-intensive systems, goats are grazed, and additional feeds are

supplemented at night. In the extensive systems, goats graze on available pasture

without supplementation.

2.2. DATA COLLECTION AND CALCULATION

In each district, we chose five households (from 60 selected households) with

cassava cultivators at eight months after growing and an area of 1000 m2/plot to

collection and calculation of fresh cassava forage productivity. Five positions were

selected in each plot of land by diagonal method. Land area of each position was 4m2

(Total area was 4 * 5 = 20m2). In each position, all cassava plant was cut and weighed

(except root). Cassava plants were the whole plant above the soil. Cassava plant was

divided into two parts: Cassava forage – which were two thirds of the above ground

part of cassava plant (red line on the right in Figure 2.1); weighed the cassava forage

(1); and hard stems (blue line on the right in figure 2.1) - which was one third above

soil level, weighted them (2).

In this case, cassava forage was defined as below that and it was described in

figure 2.2. Cassav forage was cassava livestock feed. Cassava forage was divided into

two parts: (3) Tenderstems + (4) leaves (including peiole).

Tenderstems were called cassava stems (3)

Weight of cassva plant = (1) + (2)

Weight of cassva forage (1) = (3) + (4)

The yields of of fresh cassava forage, cassava stems and cassava leaves

(including petiole) were calculated by green matter per hectare. The yield of dry matter

was calculated by the fomula: Yield of dry matter (tons/ ha) = % dry matter * the yield

of green matter (Tu Quang Hien, 2015)

Figure 2.1. Cassava plant parts

Figure 2.2. Cassava forage parts

Chemical compositions of cassava forage and stems were analyzed as dry

matter (DM), crude protein (CP), organic matter (OM), acid detergent fibre (ADF),

neutral detergent fibre (NDF), Hydrogen cyanide (HCN) and total tannin.

2.3. CHEMICAL ANALYSIS

All samples of cassava forage and stems were analyzed for DM, CP and ash

using procedures described by AOAC (1990). ADF and NDF were analyzed according

to Van Soest and Robertson (1991). HCN and total tannin were analyzed according to

ISO 6703-1:1984 (TCVN 6181:1996), AOAC 955.35. by AOAC (2016).

2.4. STATISTICAL ANALYSIS

Data was collected, preliminary calculations performed and stored in the

Microsoft Office spreadsheet EXCEL 2010. Data were analysed using General Linear

Model (GML); the basic model for analysis of variance (ANOVA); the constants

described as averages, the standard deviation was performed on the MINITAB

statistical software 16.

3. RESULTS AND DISCUSSION

3.1. CASSAVA PRODUCTION IN AN GIANG PROVINCE

3.1.1. The production and yiled of cassava

The plant area of cassava in An Giang province is shown in table 2.1

Table 2.1. Plant area of cassava in An Giang from 2014-2017

Year

2014

2015

2016

2017

Area of agricultural land (ha)

298,560

297,872

297,490

297,872

Plant area of cassava (ha)

816

701

1,335

1,400

Yield (tons/ha)

23.8

22.0

19.8

20.5

Production (thousand tons)

19.4

15.3

26.3

28.7

Source: Statistical yearbook of An Giang 2018

The plant area of cassava doubled from 2014 to 2017, at the root harvesting, 9

1 (Mui, 1994). It is estimated that about 7.000 tons of cassava foliage are produced in

to 10 months after planting, the foliage production can be about 5 tonnes dry matter ha-

An Giang province as a by-product of root harvesting. Cassava foliage is recognised as

a source of undegraded protein with a high content of digestible nutrients for both non-

ruminants and ruminants (Wanapat, 2001). The foliage can be used as a supplement for

animals in either fresh or wilted form or as hay (Phengvichith and Ledin, 2007;

Wanapat et al., 1997). In fact, cassava forage in An Giang province was thrown away

after root harvesting, because farmers did not know how to use it for animals and also

cassava forage contains of cyanogenic glucoside, mainly linamarin and lotaustralin

(Alan and John, 1993). Hydrolysis of these cyanogenic glucosides liberates hydrogen

cyanide (Poulton, 1988) and causes toxic symptoms in animals when they exceed the

tolerated dose. This is also one of reasons that farmers did not use cassava forage as

goat feed.

3.1.2. Plant area of cassava by district from 2014-2017

An Giang province is a one of two provinces in the Mekong Delta with hills and

moutains. Hilly land is 29,320 ha, 8.6% of total area. The hilly lands are concentrated in

Tri Ton and Tinh Bien district and one part of Thoai Son district, and this area was

planted with cassava. Plant area of cassava in Tinh Bien district was more than Tri Ton

district. Because Tri Ton district area is primarily low land and submerged by flooding.

Specially, there is flooding every year from July to November.

The results showed that plant area of cassava in An Giang was focused in two

mountain districts (eg: Tri Ton and Tinh Bien) (table 2.2), the remaining districts grew

a little or no cassava. Because the soil in these areas was poor, and did not have enough

water in dry season, only cassava is suitable in those districts. Cassava growing in two

districts was for its root only, a little stem was kept for next planting, and almost all

cassava forages were thrown away or burned for household activities. Meanwhile, feed

resources for ruminants are not enough when rain or flooding comes.

There are two varieties of cassavas in this area: Sweet cassava “Mi Ke”, that is

local variety grown in Tri Ton district. Sweet cassava root is useful fresh food or

human consumption. Second, bitter cassavas were grown in Tinh Bien district, they

were “KM94” breed cassava to be used by farmers regularly.

The “Sweet or bitter” cassava base on Cyanogenic potential cassava root.

"Sweet" is low- cyanogenic potential (CNP) cassava (root CNP less than 50 mg kg-1 as

HCN fresh weight basis) and is generally considered safe for consumption with only

basic processing (e.g., peeling and cooking), whereas "bitter" or high-CNP cassava

(root CNP greater than 100 mg kg-1 as HCN fresh weight basis) must be processed

prior to consumption to eliminate the cyanogens or reduce them to physiologically

tolerable levels (Cooke 1983; Dufour 1988a). Other reports have shown that

cyanogenic glicosides concentrate in the roots. Sweet cassava has HCN concentrations

below 100 mg HCN kg–1 and bitter cassava show concentration above 100 mg kg–1

HCN (McKey et al., 2010). Cassava plants are generally categorised as bitter or sweet,

depending upon their cyanide content. The low-HCN, or sweet cassava, has less than

50 ppm of cyanogenic equivalents, while the high-HCN, or bitter cassava has more

than 100 ppm (Wilson and Dufour, 2002).

Table 2.2. Plant area of cassava in An Giang province

Unit: ha

Year

District

2014

2015

2016

2017

Long Xuyên

Tri Tôn

263.8

189.2

248.5

475

Tịnh Biên

547.5

507.4

1,076.9

903.8

Thoại Sơn

1.5

An Phú

Total

816.3

700.6 1,335.4

1,400.3

Source: Statistical yearbook of An Giang (2018)

3.1.3. Yield of cassava with different of variety in An Giang

The yield of cassava plant is shown in table 2.3. The yield of cassava plant was

different between sweet cassava and bitter cassava. The yield of sweet cassava forage

was higher than bitter cassava variaty. The effect of plant population density on cassava

forages production was investigated by Meyelles et al. (1977) and in studies of Khang

et al. (2004), Hue et al. (2012) it was reported that the yield of cassava forage was

affected by the variety, plant age and season. Furthermore, the differences in DM

forage yield could be due to the differences in soil, fertilization (Molina and El-

Sharkawy, 1995), age at first cutting and interval between cutting (Lokard et al., 1985;

Tung et al., 2001; Hong et al., 2003)

Table 2.3. Yield of cassava with different variety in 2017

Yield of cassava (tons/ha)

Variety of

cassava

Tubers

Plant (in fresh)

Plant (in DM)

Sweet

17.4 ± 6.8

39.4 ± 10.8

11.2 ± 3.0

Bitter

21.8 ± 7.6

31.9 ± 8.3

10.3 ± 2.7

* Estimated yield

3.1.4. Planted area and the purposes of cassava cultivation

A preliminary survey planting area of cassava cultivation is shown in table 2.4.

Tri Ton and Tinh Bien districts are mountainous districts of An Giang province,

specially Tri Ton district which has both mountains and lowlands also, and in which

ethnic minorities are the majority (about 32%) and the percentage of poor households

accounts for 50%; The area of unused land is quite large: 18,568 ha (Statistical

yearbook of An Giang, 2017). The economy of the local people relies heavily on

agricultural production. With the natural conditions and topography of the highlands,

agricultural production in these two districts is strongly influenced by the water used in

cultivation. There is a general lack of water in the dry season because the water source

is mainly rainy. The educational level of local people is relatively low, backward

farming practices lead to low economic efficiency compared to the potential of

agricultural production in the region. Therefore, the research on agriculture, cultivation

and livestock development is the basis for planning and effectively using local land and

water resources, contributing to stabilizing and improving the lives of local people (Le

Van Khoa et al., 2012).

Table 2.4. Plant area of cassava cultivation in An Giang

Tri Ton

Percentage,

Tinh Bien

Percentage,

(n=60)

%

(n=60)

%

Plant area (ha/farm)

3.3 ± 3.9

2.28 ± 2.5

Yield of tubers (ton/ha)

17.4 ± 6.8

21.8 ± 7.6

Variety of cassava

Bitter cassava (farms)

0.0

100.0

Sweet cassava (farms)

100.0

0.0

The purposes of growing cassava

Using cassava root for

100.0

0.0

human food (farms)

Sell cassava tubers to company

0.0

100.0

(farms)

0.0

Using for animals (farms)

Cassava root

0.0

3.33

Cassava leaves

0.0

0.00

Cassava forage

18.3

21.7

0.0

75.0

Using stems for planting (farms)

The main crop in the study area is rice (1 crop / year) in the rainy season, the

farmers also plant a number of vegetable crops such as peanuts, green beans, sesame,

vegetables of all kinds at the beginning of the rainy season. Crop productivity and

efficiency of agricultural production in lowland areas is sub-opimal beacuse local

people cultivate traditionally, and have not applied many scientific and technological

advances to production. The purpose of growing cassava here is mainly to sell tubers

(fresh or dried tubers root sold to traders), a litle of cassava stems was kept for next

growing, and cassava forage were thrown away in the field or burning.

3.1.5. Evaluation of chemical composition of cassava parts

The chemical composition of cassava forage and cassava stems were

differences and showed in table 2.5.

Table 2.5. Chemical composition of cassava parts

% DM

Variety of

DM,

HCN

Total

cassava

%

(mg/kg FW)

CP

NDF

tannin

Bitter cassava

26.8

13.4

49.4

4.6

153

Cassava forage

Sweet cassava

21.7

13.8

47.0

3.1

34.5

Bitter cassava

31.5

4.9

66.1

1.6

68.0

Cassava stems

Sweet cassava

24.5

6.1

65.8

1.3

30.5

Notes: FW: fresh weight

DM: Dry matter, CP: crude proetin, NDF: neutral detergent fiber, HCN: Hydrogen cyanide

The crude protein of sweet cassava forage was not different between 2 cassava

varieties, but CP content in cassava stems was different. Crude protein content of

cassava forage ranged from 13.4 to 13.8 % on DM basis. These reults were lower than

the results of 18.8% reported by Man and Wiktorsson (2001); and 17.7 to 22.6%

reported by Khang et al. (2005). Estimated protein yield in the present study ranged

from 0.53 to 0.83 tonnes ha-1 about 11 months of growth. The differences in results are

probably due to the differences in the variety, soil fertility, harvesting time, climate

(Moore, 1976; Khang et al., 2004).

3.1.6. The fresh and dry yield of cassava proportion with different variety

In the present study, after root harvesting, there was cassava plant remains.

Cassava plants were divided into two parts: hard stems (one third above the soil of

cassava plant) and cassava forages (two third of aerial part of cassava plant). It was

described in Figure 2.1 & 2.2). The fresh and dry weight proportion of cassava plant is

shown in table 2.6. The cassava forage was differences between two varieties of

cassava. The proportion of sweet cassava forage was higher than the bitter cassava. The

reason is that the harvesting time of bitter cassava was a long time after planting (10 –

12 months) while, the harvesting time of sweet cassava was 6-8 months, the plant has

more leaves, shorter and softer stems. The mean dry leaf proportion of sweet cassava

forage was high (51.7%) similar to an earlier study by Meyrelles et al. (1977), the leaf

propostion of cassava forage on DM basic was almost 52%, but it was slightly lower

than found in study result of Khang et al. (2004) (59%). These results were different

due to the differences in variety, farming conditions, regions, soil, and fertilization and

cutting time.

Table 2.6: Yield of cassava proportion with different variety

Sweet cassava

Proportion

Bitter cassava

Proportion

(tons/ha)

%

(tons/ha)

%

Fresh cassava plant

13.2 ± 3.6

33.5

17.2 ± 4.5

54.0

Hard stems

26.2 ± 7.2

14.7 ± 3.8

66.5

46.1

Cassava forage

8.7 ± 2.4

4.9 ± 1.3

22.1

15.3

Cassava stems

17.5 ± 4.8

9.8 ± 2.5

44.4

30.7

Leaves + petiole

DM cassava plant

5.5 ± 1.5

6.4 ± 1.6

49.1

62.1

Hard stems

5.7 ± 1.6

3.9 ±1.0

50.9

37.9

Cassava forage

2.1 ± 0.5

1.2 ± 0.3

18.4

11.3

Cassava stems

3.6 ± 1.0

2.7 ± 0.76

32.5

26.6

Leaves + petiole

CP of cassava forage

0.79 ± 0.23

0.52 ± 0.15

in DM (tons/ha)

3.2. GOAT PRODUCTION IN AN GIANG PROVINCE

3.2.1. Ruminants population in An Giang from 2014- 2017

Goat production in An Giang increased 3.2 times from 2014 to 2017. The

reasons for this increase were that goat are easy to raise, are a low investment, there is

an increasing price and increasing consumption of goat meat, in not only An Giang but

also in the whole country.

Table 2.7. Population of ruminants in An Giang from 2014- 2017

Unit: heads

Year

Ruminants

2014

2015

2016

2017

Goat

4,325

7,876

11,905

13,950

Cattle

109,306

111,709

96,040

81,543

Buffalo

4,181

4,013

3,876

3,265

Source: Statistical yearbook of An Giang 2018

In recent years, goat production in An Giang is shown in table 2.7. Based on the

survey, the climate, weather and natural conditions were suitable for developing goat

raising. The total area of hilly land in An Giang is about 29,320 ha, accounting for

8.6% of the total land area of the province. There are natural grass and agricultural by-

products all year round, there is a clean water source, farmers love raising and goat

raising, therefore, goats were raised a long time ago in An Giang. However, goat

raising is still not much developed, because goats were raised by traditional farming,

farmers did not utilize by-product efficiency.

Goats were raised and concentrated in the Phu Tan - Tan Chau districts to the

mountainous areas of Tri Ton and Tinh Bien. Currently, the goat production in 2017

was 13,950, the most was in Tinh Bien (2,428); Tri Ton (2,245) (Statistical An Giang

yearbook, 2018). The number of goats in 2017 increased by 3.2 times compared to

2014, because the price of goats in the market increased sharply, while households with

more than 20 heads / household accounted for 49.2%.

3.2.2. Goat farm size and purpose raising in An Giang province

Base on the survey results, the farm size and structure of goats in the Tinh Bien

and Tri Ton districts are presented in table 2.8.

The goat farm size were divided into three groups: the group of raising

households below 10 accounts for the lowest percentage, the number of households

raising over 20 heads accounts for a high percentage (59%), this result was higher than

the research results of Nguyen Binh Truong (2016) goats raised in Tinh Bien district

were 26.7% with households raising more than 20 heads per household. Thus, Goat

breeding in An Giang, especially Tinh Bien area developed and increased clearly.

Table 2.8. Farm size and purpose raising

Tri Ton

Tinh Bien

percentage

Total

percentage

Items

%

Number

%

Farm size (Household)

1-<10 heads/farm

23.3

8.3

15.8

35.0

10-20 heads/farm

31.7

66.7

49.2

> 20 head/farm

Purpose raising (Heads)

62.9

1,163

95.1

691

Meat

1,854

79.8

37.1

4.9

408

Breeding

468

20.2

1,099

1,223

Total

The purpose of raising goats here was mainly to sell meat at 79.8%, in addition

to raising goats with the purpose of selecting good ones in the herd to sell goats for

local market, or neighbourhood; but account for a smaller percentage (20.6%). In

addition, markets for goat production (eg: milk, cheese, ...) are in the cities providing

farmers with better income and opportunities for further development (Nguyen Van

Thu, 2016). There is a high demand for goat meat in many different areas of Vietnam

from the North to the South and the rate of increase in the number of goats annually is

not sufficient to meet the demand. Therefore, many farmers and companies are

preparing to build large commercial farms with the importation of dairy goat breeds for

both milk and meat.

3.2.3. Goat prodution systems in An Giang

The results in Table 2.9 showed that goats were raised intensive, semi- intensive

and extensive systems and intensive was highest (55%).

Table 2.9. Goat production systems in Tri Ton and Tinh Bien district

Number of farms in district

Percentage,

Tinh

Percentage,

%

Management

Tri Ton

%

Total

Bien

Intensive

51.7

58.3

55.0

Semi-intensive

45.0

41.7

43.3

Extensive

3.33

0.00

1.67

Intensive systems are the main method of goat raising in An Giang, this result

was similar to the results of Nguyen Binh Truong (2016) who found raising goats by

intensive systems was 66.7%. This systems of complete confinement helps the farmers

manage each individual, can detect disease or manage oestrus in a timely manner, but

feed had to controled actively, while semi- intensive systems help goats have time to

graze, develop the right features and reduce the reserve of food. According to the study

of Bounmy and Nguyen Xuan Trach (2010) in Laos, semi-grazing is the most common

farming method, accounting for 100% of the surveyed households. By- products,

storage or processing of goat feed reserves have not been considered. Goat grazing is

restricted in farming areas because goats are destructive, eating a variety of foods

affecting other households' crops. Although raising by completely captive raising

methods, the farmers in the surveyed areas still raise their livestock in the traditional

way, around the farming area, there were any kind of edible plants that can be used, not

interested in the demand. Nutrition for goats, how to coordinate, reserve feed sources

for goats to ensure nutritional needs according to each stage of their development are

not of interest in this system. In addition, extensive farm is causing increase green

house gas (GHG) emissions as Alexandra and Irene (2015) reported that GHG

emissions were particularly high in the extensive farm, because of its low productivity

and the excessive use of pastures in livestock feeding. Therefore, intensive systems can

manage feed and limite methane emissions from ruminants.

3.2.4. Feed and feeding systems

Goat feed is very diverse in Tinh Bien and Tri Ton district, beside natural grass,

there are many kind of leaves, eg: jackfruit leaves, magic vegetables, banana leaves,

peanuts, and sweet potatoes, but limited in quantity. In the survey area, the main feed is

natural grass, 100% of the households use natural grass and a source of locally

available by-products except cassava leaves. Few households (21.7%) among surveyed

households grew grasses: elephant grass, VA06 grass to supplement feed in the dry or

flooding season or at harvest time. In addition to the main feed source of natural grass

and seasonal byproducts, a few households had supplied salt (38.3%), rice bran

(18.3%); very few households used concentrate supplement, all fewer households

(35%) did not supply supplements. The farmers did not care about quaities or chemical

composition of grass or by-product, so they did not supply enough nutrition for their

goats, especially in the dry season (from February to May). The results were slowly

growth rate, and low production. Beside that, the nutritional supplement, especially

protein sources, mineral, visibly improve productivity of goats (Phengsavanh, 2003;

Keopaseuht et al., 2004; Bounmy Phiovankham and Nguyen Xuan Trach, 2011).

Table 2.10. Feed and feeding systems for goats in Tri Ton and Tinh Bien district

Tri Ton

Tinh Bien

percentage,

Household

Items

%

Feed

Natural grass

100

Natural grass + Leaves (except CL)

6.67

Natural grass + by-products

46.7

Natural grass + cassava forage

6.67

3.33

Natural grass + Grass growing

21.7

Natural grass + Commercial concentrate

8.33

Supplements

Salt

25.0

38.3

Rice bran

15.0

18.3

Commercial Concentrate

8.3

8.33

No supplement

51.7

35.0

Note: CL: cassava leaves

3.2.5. Diseases and diseases management

The survey results of 60 households raising goats in 2 districts (Table 2.11)

show that 50.8% of total households have never used vaccines for goats. The most

common disease for goats was often diarrhea (26.9%), other disease eg: coughing,

sneezing and rumen bloating, accounting for 23.4%. Although there are veterinary

facilities in the communes of the two districts surveyed for animals welfare, the farmers

used less vaccine to prevent diseases. Farmers often bought drugs for injection those

diseases such as diarrhea, fever and cough. In recent years, there have been occasional

illnesses such as mouth ulcers. People often used traditional method such as finding

some leaves to apply to ulcers. For other diseases such as rumen bloating, and mastitis

most farmers have not found any cure for goats. This is causing low goat production.

Table 2.11. Diseases and diseases management of goats

Tri Ton

Tịnh Bien

Diseases and

Percentage,

Total

percentage,

management

%

Household

%

Diseases

4.9

5.6

5.3

Parasites

18.3

14.6

16.4

Mouth ulcer

30.5

23.6

26.9

Diarrhea

Infectious

18.3

15.7

diseases

6.1

15.7

11.1

Difficult birth

Others (cough,

24.7

23.4

Sneeze, rumen

bloating;,...)

Diseases management

28.3

46.7

37.5

Vaccine

61.7

40.0

50.8

No vaccine

10.0

13.3

11.7

Deworming

4. CONCLUSIONS

In An Giang province, goat production is developing with promising conditions

of abundant feed resources, good government policies, improved research results, good

markets and efficient development strategies. However, some constrains for production

development such as low breed quality, lack of large farms and improving nutrient of

feed, limited knowledge, poor marketing and less international co-operation should be

improved for a sustainable goat production and dairy goat production also. Beside that,

cassava forage has potential in An Giang. The average of dry matter cassava forages

was 5 ton/ha in 2017. They can be used as a protein source, as a replacement for grass

for ruminants but farmers did not use because it is high HCN content. How to use and

preserve cassava (including the stems) as feed ruminants and against toxicosis by

reducing HCN content. The other thing, after a few days root harvesting, leaves will

fall down, cassava stems were only remaining. Based on that situation, the study of

utilizing is not only cassava forage, but also cassava stems necessary and practically by

alkaline method. Therefore, the interest in using urea treated cassava stems could be

improved with improved nutritive value and preservation.

REFERENCES

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Keopaseuht T., Ty C., Bounthong B., Preston T. R., 2004. Effect of method of offering forages of Gliricida sepium and Stylosanthes guianensis CIAT 184 (Stylo) to goats on intake and digestibility. Livestock Research for Rural Development 16.

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Man N. V. and Wiktorsson H., 2001. Cassava tops ensiled with or without molasses as additive effects on quality, feed intake and digestibility by heifers. Asian-Aust. J. Anim. Sci. 14:624-630

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CHAPTER 3 USING UREA TO TREAT CASSAVA STEMS AND EFFECT

OF WATER SPINACH AND BIOCHAR ON FEED INTAKE,

DIGESTIBILITY AND N-RETENTION IN GOATS FED

UREA TREATED CASSAVA STEMS

Abstract

The specific objectives were to determine what level of urea treated cassava

stems would facilitate the storage, improving nutritive value and the same time improve

its digestibility. Then, determining the synergistic effect of biochar and water spinach

on growth of goats fed urea treated cassava stems. There were two experiments:

Treated cassava stems with 5 levels of uera (0; 1; 2; 3; 4 % in DM) as treatments and 4

replications. All treatments were kept in anaerobic conditions. Treated cassava stems

appearance characteristics were observed, pH value, HCN, tannin content and chemical

composition were measured at the storage times (0; 2; 4; 6 and 8 weeks). The results

were that with 8 weeks storage, urea treated cassava stems were preserved of high

quality in the evaluation of color, ammonia, mold appearance, and pH. Cassava stems

treated with 3% urea level in DM had improved nutrient value. Urea treatment of the

cassava stems increased the crude protein from 5.5 to 11.7% in DM and urea treatments

were effective in delignifying HCN content of cassava stems. Moreover, this level of

urea is needed to prevent mould in cassava stems ensiled with urea. The 3 % level of

urea in DM was the best treatment and chosen for the next experiment.

Four “Bach Thao” goats (LW 14 ± 2 kg) were fed urea-treated cassava stems

alone (UCS) or with a supplement of water spinach at 1% of LW (DM basis) (UCSW),

with biochar (derived by carbonization of rice husks in an updraft gasifier stove) at 1% of

DM intake (UCSB) or with water spinach + biochar (CSWB). The design was a Latin

square with four treatments and four periods, each lasting 15 days (ten days for

adaptation and 5 days for collection of faeces and urine). DM intake was increased 18%

by supplementing the urea-treated cassava stems with biochar. Addition of water spinach

increased total DM intake by 25% while the combined effect of biochar plus water

spinach was to increase intake by 41%. Biochar increased daily N retention by 46% and

the biological value of the absorbed N by 12%.

Key words: Cassava stems treated, prevering, biofilms, biological value, N-retention

1. INTRODUCTION

Cassava (Manihot esculenta Crantz) is a perennial woody shrub of the family

Euphorbiaceae. It originated in the Caibbean and South America and is extensively

cultivated as an annual crop in the tropics and sub-tropics for the dual purpose of

tuberous roots for human consumption and roots and forage as a feed for animals.

Cassava forage is recognized as a source of bypass protein with a high content of

digestible nutrients for both non-ruminants and ruminants (Wanapat 2001). The forage

can be used as a supplement for animals in either fresh or wilted form or as hay

(Phengvichith and Ledin, 2007; Wanapat et al., 1997). At root harvest, 9 to 10 months

after planting, the forage production can be about 5 tonnes dry matter/ha (Mui, 1994). It

is estimated that more than 2.5 milion tonnes of cassava forage are produced in Vietnam,

of which about 15,000 tonnes are in An Giang, Cassava forage is usually thrown away

after harvesting the root, because of its content of cyanogenic glucoside, mainly

linamarin and lotaustralin (Alan and John, 1993). Hydrolysis of these cyanogenic

glucosides liberates hydrogen cyanide (HCN) (Poulton, 1988) and causes toxicity

symptoms in animals when the tolerated dose is exceeded.

Cassava forage consists of the leaves, petioles and small branches which attach to

the highly lignified stems. Observations at the Rabbit and Goat Center in Bavi, North

Vietnam indicated that the stems were well appreciated by goats and this led to the

experiment reported by Thanh et al. (2013) in which chopped cassava stems supplemented

with fresh cassava forage supported live weight gains in growing goats of 57 g/day, 100%

higher than when Guinea grass was used to supplement the cassava stems.

Since the use of urea (CO(NH2)2 for straw treatment has been widely studied

and proved to be effective in the Tropics (Schiere and Ibrahim, 1989; Chenost and

Kayouli, 1997; Trach et al., 2001; ThuyHang el at., 2005), 3 or 4% urea – treated straw

viewed as a positive control together with untreated straw being the negative control in

the present studies to evaluate other treatments. According to Thanh et al. (2013),

cassava stems contain 33% DM but only 5.5% crude protein (CP) in the DM. It was

therefore hypothesized that there could be a double benefit from ensiling the cassava

stems with urea: (i) to provide the ammonia needed by rumen organisms; and (ii) to

improve the digestibility of the stems DM as has been widely proven in the urea-

ensiling of low-protein, fibrous feeds such as rice straw (Trach et al., 1998). Major

advances have been made recently in the integrated use of the cassava plant as a means

of intensifying for ruminant livestock production. In a follow-up series of experiments

it was shown that fresh cassava forage could replace the major part of the brewers’

grains as bypass protein source, provided that a small amount of brewers’ grains (4 to

5% of the diet DM) was retained apparently acting as a “prebiotic” to counteract the

potential toxicity of the HCN released from the cyanogenic glucosides in the cassava

forage (Inthapanya et al., 2016; Binh et al., 2017). The systems were further developed

to use ensiled cassava root as the carbohydrate energy source with a local “rice wine”

byproduct replacing the brewers’ grains as the source of prebiotic (Sengsouly et al.,

2016; Inthapanya et al., 2017).

An experiment with growing goats fed almost exclusively (95% of the diet DM)

on fresh cassava forage (Sina et al., 2017) confirmed the vital role of the small

supplement of brewers’ grains’ in a cassava-based feeding system. Growth

performance was more than doubled from 65 to 160g/day when the brewery byproduct

was included at 5% of the diet DM. Increased understanding of the role of prebiotics as

support for biofilms and their associated microbial communities involved in the

animal’s digestive systems led to an appraisal of the potential role of biochar as a

prebiotic, following it’s known ameliorating properties in soils (Lehmann, 2007;

Preston, 2015) thought to be due to its interactive role in supporting microbial

communities in this medium.

In an initial study with 1% biochar in the diet (Leng et al., 2012), growth rates

were increased 20% but were probably constrained by errors in management of the feed

resource (fresh cassava root) that probably propitiated growth of mycotoxins (R A

Leng, personal communication). More recent studies have shown synergistic effects

from combining biochar with rice distillers’ byproduct in a cassava-based diet for

fattening cattle (Sengsouly and Preston, 2016) and by combining biochar with water

spinach in diets of goats (Silivong and Preston, 2015, 2016).

treated cassava stems that would facilitate the storage and at the same time improve its

digestibility. Then, determining the synergistic effect of biochar and water spinach on

With this background, the specific objectives were to determine the level of urea

growth of goat fed urea treated cassava stems, shown to be a potential feed resource for

goat by Thanh et al. (2013).

2. MATERIALS AND METHODS

The experiment was conducted at An Giang University farm, An Giang

province, Vietnam. There were two experiments.

2.1. EXPERIMENT 1

The treatments had five levels of urea (0, 1, 2, 3 and 4%, DM basis) added to

freshly chopped cassava stems; and five storage times (0, 2, 4, 6 and 8 weeks). Each

treatment combination was replicated 4 times. Two tonnes of cassava stems were

collected from farmers’ fields directly after root harvesting; and chopped by hand.

Representative amounts were analyzed for DM by infrared radiation (Undersander et

al., 1993) prior to hand mixing 20 kg quantities with the indicated amounts of

crystalline urea followed by storage in polyethylene bags which were then sealed.

Urea treated cassava stems were prepared as below:

1. Sweet Cassava stems were harvested from farmer’s cassava field after root

harvesting

2. Cassava stems were chopped (5-10cm) by hand.

3. The chopped cassava stems were weighed, then thoroughly mixed with

different level urea at 0,1,2,3 and 4% in DM.

4. The mixture was put in polypropylene plastic bag (60 cm width by 80 cm

length: 20kg) and compacted to expel air.

5. The bags were tightened using rubber bands and stored at room temperature.

The treatments were allocated in a completely randomized design and 4

replications. A total of 100 bags were used.

The mean DM of the untreated cassava stems used in the preservation process

was the mean of all samples measured by quick microwave dryer measurements

(Undersander et al.,1993) directly before the preservation. After preservation for 0; 2;

4; 6 and 8weeks samples of cassava stems treated with urea were taken for evaluation of

physical appearance characteristics, measurement of pH, chemical composition and in a

comparative study on DM degradation with untreated cassava stems. Twenty samples in

opening the plastic bag the cassava stems were first assessed in terms of color and

smell. Mould growth was graded based on the moulded proportion of the cassava

stems sample. The smell and color of cassava stems treated were evaluated based on the

each period of storing were observed for fungus development, smell, and color. After

smell and color of the freshly untreated (table 3.3). The pH values of the samples were

measured immediately after sampling by a pH meter (ORION model 420 A).

Table 3.1. The chemical composition of cassava stems before treating in experiment 1

Chemical composition

%/ kg DM

DM (%)

23.6

CP (% kgDM)

6.14

ADF (% kgDM)

50.7

NDF (% kgDM)

65.5

OM (% kgDM)

89.3

Tannin (%)

1.25

NH3

0.00

HCN (mg/kgFW)

34.5

6.40

2.2. EXPERIMENT 2

The best of urea level treated cassava stems as feed for goats was chosen

following the results of experiment 1.

Feed and feeding

The cassava (sweet variety) was grown in sandy soil in the An Giang University

farm. from January to August 2015. It was fertilized (per ha) with 8 tonnes of cattle

manure, 175 kg urea, 200 kg Super-phosphate and 130 kg potassium chloride.

The cassava stems (no leaves; Figure 3.1) were harvested at 40-50cm above

soil level at intervals of 150 days when it had attained a height of 100 - 120 cm. The

cassava stems were chopped by machine (Figure 3.2), mixed with urea (3% DM basis;

no water was added) and ensiled in plastic bags after first extracting the air (Figure

3.4). They were ensiled for 21 days (Figure 3.5), after which they were fed ad libitum

as the basal diet of the goats (Figure 3.6).

Figure 3.1. Freshly

Figure 3.2. Chopping into 5-10

Figure 3.3. Urea added at 3%

harvested cassava stems

cm lengths

of stems DM

Figure 3.4. Chopped

Figure 3.5. Urea-treated stems

stems-urea are put in

are stored for 21 days

stems after 21-day storage

polyethylene bags and the

ready for feeding

air extracted

Figure 3.6. Urea-treated

Experimental design

Four “Bach Thao” goats (14 ± 2 kg) were fed urea-treated cassava stems alone

(UCS) or with a supplement of water spinach at 1% of LW (DM basis) (UCSW), with

biochar at 1% of DM intake (UCSB) or with 1% water spinach + 1% biochar (CSWB).

The design was a Latin square (Table 3.2) with four treatments and four periods, each

lasting 15 days (ten days for adaptation and 5 days for collection of faeces and urine).

Between each period there was a period of 7 days for resting during which time they

were fed the diet destined for the subsequent period of the experiment.

Table 3.2. The layout of the experiment

Period

Goat 1

Goat 2

Goat 3

Goat 4

UCS

UCSB

UCSW

UCSWB

UCSW

UCSWB

UCS

UCSB

UCSWB

UCS

UCSB

UCSW

UCSB

UCSW

UCSWB

UCS

Animals and management

The goats were housed in metabolism cages made from bamboo, designed to

collect separately faeces and urine. They were vaccinated against Pasteurellosis and

Foot and Mouth disease and treated with Ivermectin (1ml/10 kg live weight) to control

internal and external parasites. They were weighed between 06:30 and 07:30h before

feeding at the start and end of each experimental period.

Feeds and feeding

The biochar was made by burning rice husks in a top-lit, updraft (TLUD)

gasifier stove (Olivier 2010) (Figure 3.7). To reduce the “dusty” nature of the biochar it

was mixed with a small amount of water enough to moisten the biochar but avoiding

any excess. The chosen amounts were offered twice daily in troughs separate from the

cassava stems (Figure 3.8) and water spinach.

stove (Olivier)

Figure 3.7. The biochar was the residue from rice husks used as fuel in a gasifier

Figure 3.8. Biochar, water spinach and urea-treated cassava stems were fed in

separate troughs

Water spinach was collected daily from natural stands in the University campus.

Harvesting of water spinach was done 10 -12h prior to each feed, morning and afternoon.

Water spinach was chopped by hand prior to being put into the feed troughs. The chosen

amounts were offered twice daily in troughs separate from the cassava stems.

Feed refusals were weighed every morning prior to giving the new feed. Samples of each diet component were taken daily, stored at -180C, and bulked at the

end of each period for analysis.

Digestibility and N retention

During the data collection periods, the feces and urine were recorded twice

daily at 7:00 and 16:00 and added to jars containing 100 ml of 10% sulphuric acid. The

pH was measured and, if necessary, more acid added to keep the pH below 4.0. After each collection period: (i) a sample of 10% of the urine was stored at -4o C for analysis

of nitrogen (AOAC 1990); (ii) the feces were mixed and a sample (10%) stored frozen at -20oC.

Chemical analysis

Cassava stems before treating and cassava stems treated at the end of the

ensiling period, were analyzed for dry matter (DM), Nitrogen (N) and total ash using

procedures described by Official Methods of AOAC (1990). For the determination of

nitrogen content, wet samples of all types of cassava stems were taken right after

opening the bags to be acidified without drying. Acid detergent fibre (ADF) and

Neutral detergent Fiber (NDF) were determined according to Van Soest and Robertson

(1991). The pH value of the silages was recorded on fresh samples by a pH electrode

while the HCN content was determined on fresh ensiled samples by titration with

AgNO3 after boiling the sample and concentrating the HCN in KOH (AOAC, 1990).

Samples for other chemical analyses were dried at 60°C for 24 h and ground over a 1

mm screen. The DM was determined by drying at 105°C for 24h to constant weight

(method code no. 925.09 of AOAC, 1990). The CP was calculated from total nitrogen

(N x 6.25) which was determined by the Kjeldahl (method code no. 988.05 of AOAC,

1990) in dry samples. The dried samples of cassava stems, and water spinach were also

analysed for DM, CP (method 978.10 of AOAC, 1990) and HCN content (except in

water spinach and biochar). HCN content was determined according to the standard

methods of AOAC (2016). Total tannin content was determined according to the

method (955.35) of AOAC (2016). Metabolizable energy of the diet (MJ/kg) were

calculated from organic matter digestibility (OMD: %) by formula of Mc Donald et al.

(2002). The formula is: ME = 0.160*OMD. All samples were analysed in triplicate at

the laboratories of An Giang University, An Giang province, Vietnam.

Statistical analysis

Data were analyzed with the General Linear Model option of the ANOVA

program in the MINITAB software (Minitab 2016). Sources of variation were levels of

urea, storage time, random error for experiment 1. Sources of variation were treatments,

animals, periods and error for experiment 2.

3. RESULTS AND DISCUSSION

3.1 EXPERIMENT 1

3.1.1 Hygienic quality of cassava stems treated by physical evaluation

3.1.1.1 At the processing time (0 week)

Cassava stems after cutting, mixed with different urea levels according to each

treatment, were evaluated for color, and smell before putting them into the incubation

bags. Almost treatment was green color and smell of the same cassava stems.

3.1.1.2. Hygienic quality of cassava treated by physical evaluation at 8 weeks storage time.

The smell of cassava stems treated with urea increased with urea level. In

treatment 1 (0% urea), the smell of cassava stems was like the smell of cassava

fermentation stored for a long time. In the urea treatments the ammonia smell was

slight in the lower urea levels (from treatment 2 to treatment 4%). The higher the level

of urea was applied the stronger the pungent smell was found to be. It seemed that the

ammonia smell could not be graded in the 3% and 4% urea treatments.

The colour of fresh cassava stems was light green. The treated cassava stems

colour changed after treating with urea to a light brown colour in the short storage time

(4 weeks) and to a brown, dark brown colour in the long storage time (8 weeks). It is

the typical colour of urea treated fresh rice straw.

Moulds did not appear at all in any of treated cassava stems bags at the

observation 2,4 and 6 weeks after treating. At the five observations at 8 weeks after

treatment, molds were present in a low ratio in treatment 2 (1% urea) and to a slight

extent in the treated cassava stems bags of 2% urea. No moulds were seen in the other

treatments.

Based on the results of the evaluation of the physical appearance of the treated

cassava stems with respect to color, smell, and mold, the quality of treated cassava

stems in the bags or bales were considered to be good, except in the treatments 1(no

urea). Cassava stems in these treatments had no, or only a slight ammonia smell, and

some fungi developed on the surface of the bags.

3.1.1.3. pH value of cassava stems treated with different level of urea and storage times

The pH value of cassava stems treated with urea is shown in the table 3.3.

There were consistent effects of urea level on the pH in the stored stems with

curvilinear increases to maximum values after 4 weeks of storage declining

subsequently. Within storage times the pH was positively related to the level of urea

added at the beginning of storage. Present results show that when alkaline at different

urea levels, the pH value was different significant after 4 weeks storing, such as pH was

8.5 (3% and higher urea). Ammonia, released in the urea hydrolyses, and trapped in the

bag, caused an increase in straw pH to >8, that inhibits oxidative and microbial

fermentation (Wilkins, 1988) and can keep the treated cassava stems in a good

condition for a long time. On the other hand, the pH value in the incubation bags was

been actually by NH3 resolved from urea, due to water and urease of microorganisms,

urea was broken down into ammonia (Vu Duy Giang et al., 2008) So, the pH value is

not different after cassava stems treated with different urea levels at 0 weeks.

CO(NH2)2+ H2O urease 2NH3+ CO2

In the present study, most treatments with high levels of urea (3% and higher)

had a strong ammonia smell and pH values higher than 8, and the treated cassava stems

was in a good state of preservation (Table 3.3).

Table 3.3. Effect of urea level and storage time on pH in cassava stems

SEM

p-value

Urea (%)

0 6.44E

Storage time, weeks 6 4 4.81dG 5.0cFG

2 5.7cEF

8 4.5cG

0.172

<0.001

6.11F

7.16bE

7.43bE

6.74cEF

6.1bF

0.205

0.001

6.47EF

7.63abEF

7.93abE

7.46bcEF

6.1bF

0.397

0.016

6.54H

8.15aF

8.76aE

8.23abF

7.4abG

0.070

<0.001

0.109

<0.001

6.43G 0.144 0.332

8.41aE 0.206 <0.001

8.36aE 0.203 <0.001

7.9aF 0.324 <0.001

8.47aE 4 SEM 0.192 p-value <0.001 abcd Mean value in columns with different superscripts are significantly different (p<0.05) EFGH Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different.

At the lower levels of urea treatment, no or not very much ammonia was

produced and resulted in the low pH and slight ammonia smell found, especially at the

five observations, 8 weeks after ensiling. Longer storage periods with some continuous

loss of ammonia resulted in decreasing pH values, which created conditions for fungi

development. This is in agreement with Thuy Hang et al. (2005); Nguyen Xuan Trach

et al. (2006); Đang Hoang Lam (2013) reported that alkalization of agricultural

byproducts (straw, cassava stems, ..) were increase pH above 8.

3.1.2. Chemical compositions of cassava stems treated with difference levels of

urea and stored times

Cassava stems were treated with different urea levels under anaerobic

conditions and stored at room temperature. After storing 2, 4, 6, 8 weeks, we collected

samples, analyzed and chemical composition results of the treatments are shown below.

3.1.2.1. Ammonia content

Ammonia level increased massively in the second week of storage, then fell by

half at 4 weeks the levels being proportional to the amounts of urea added. The NH3

content of treated cassava stems was lowest in the treatment 1 (0.0% of urea), untreated

cassava stems were significantly different from all the urea treatments. The NH3

contents of treated cassava stems significantly increased with the level of applied urea,

and the NH3 contents of treating cassava stems was highest at 4 weeks storage time in

the same level of urea, but the difference was found in the next storage time (6; 8 weeks

storage time), the storage period significantly decreased the NH3 content of cassava

stems (Table 3.4). The increase in ammonia and in pH in the stored cassava stems is

similar to what has been reported for urea-treatment of other fibrous byproducts such as

rice straw (Thuy Hang et al., 2005; Trach et al., 1998).

Table 3.4 : Effect of urea level and storage time on ammonia in cassava stems Storage time, weeks

SEM

p-Value

Urea (%)

0.004 0.002 0.007 0.025 0.013

<0.001 <0.001 <0.001 <0.001 <0.001

4 2 0 0.03eG 0.08dF 0.03bG 0.38dG 2.04bF 0.08abK 0.62cGH 2.04bF 0.11abI 0.85bG 1.93cF 0.10abH 1.09aG 2.18aF 0.11aI 0.003 0.020 0.019 0.036 <0.001 <0.001

8 0.03eG 0.37dH 0.60cH 0.81bG 1.05aGH 0.008 <0.001

6 0.03eG 0.34dI 0.64cG 0.81bG 1.03aH 0.004 <0.001

0 1 2 3 4 SEM p-value abcde Mean value in columns with different superscripts are significantly different (p<0.05) FGHIK Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different

3.1.2.2. HCN content in cassava stems treated after storing time.

According to Khang & Wiktorsson (2006); Man & Wiktorsson (2001) reported

that ensiling has reduced HCN content in fresh cassava by 78%, wilting and sun-drying

reduced the HCN content in fresh cassava forage from 35% and 82%. Hang & Preston

(2005) and Phengvichith & Ledin (2007) showed that wilting cassava forage in the

shade reduced the HCN content by 58% and 45%, respectively. In this study, HCN

content in cassava stems treated were reduced also after storing time, such as HCN

content in cassava stems treated with urea at 1 & 2 % were reduced 67.5 & 68.2 %, and

at 3 & 4% of urea level, reducing 73.9% & 74.9% of HCN content after 4 weeks

preserving, it is significant when compared with fresh cassava stems (p<0.001) (Table

3.5). The different environmental temperatures, pH value to which the forages were

subjected during processing could be the cause of variations in HCN reduction.

According to Achidi et al. (2008), free cyanide evaporates at a temperature of 25C and

the cyanogenic glucosides in the cassava leaves were reduced by almost 50% when

heated at 60C for 30 minutes, and Sreekariyam (2000) showed that pH>7 cyanohydrin

acetone will degrade to acetone and HCN. I suggest that this is the reason that HCN

content was reduced in cassava stems after alkaline conditions.

Table 3.5. Effect of urea level and storage time on HCN (mg/kgDM) content of cassava stems.

Storage time, weeks

Urea (%)

0

2

4

6 SEM

8 p- value

146.9E

111.2aF

69.6aG

46.6H

2.103

<0.001

0

146.8E

108.3aF

47.6bG

0.794

<0.001

1

136.7E

96.3bcF

43.4bG

1.46

<0.001

2

147.7E

98.8bF

38.5cG

1.219

<0.001

3

142.8E

95.8cF

35. 7cG

0.571

<0.001

4

2.576

0.715

1.038

0.879

SEM

0.044

<0.001

p-value Notes: ND: No detect abc Mean value in columns with different superscripts are significantly different (p<0.05) EFGH Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different

HCN is a major factor affecting the use of cassava by-products as animal feed.

HCN is a product of hydrolysis of cyanogenic glucoside when plants suffer from

physical effects that disrupt cell structure (Speijers, 1992) and could be toxic to

ruminant when HCN ingestion of 2-4 mg /kg live weight by Makkar (1991), and Le

Duc Ngoan et al. (2004). In this result, the HCN content in cassava stems treated with

2% or higher urea level after 2 weeks storing was lower than 100mg/kg DM (from 95.3

to 98.8mg/kgDM), and lower than 50mg/kgDM after 4 weeks storing (35.6 –

43.4mg/kgDM). This means that the goat (20kg live weight) will eat 19.9 to 24.3mg of

HCN (equivalent to 1-1.2mg / kg of LW), which is not yet enough to be toxic for goats.

The decrease in HCN with storage time may similarly be he result of the high pH

(>7.00) following 2 weeks of storage with urea and would appear to be related to

chemical reactions resulting in neutralization of the hydrocyanic acid by the ammonia.

A decrease in HCN toxicity has been reported as a result of increasing the pH of the

medium (Huertas et al., 2010).

3.1.2.3. Tannin content in cassava stems treated after storing time.

Alkaline method also has observed reduced tannin content. The content of

tannin was reduced after 4 weeks of storage and the effect tended to be greater with

higher levels of urea (Table 3.6). The decrease in tannin with urea treatment is likely to

be a result of the high pH caused by conversion of ammonia from urea (Price et al.,

1979; Makkar 2003a,b). Tannins are easily oxidized at alkaline pH values to quinines,

which may promote covalent bonds to other compounds (Rawel et al., 2000).

Table 3.6. Effect of urea level and storage time on tannins in cassava stems

Storage time, weeks

Urea (%)

SEM

p-value

0

2

4

6

8

1.25

1.21

1.22a

1.26a

1.24a

0.021

0.534

0

1.20

1.00b

1.10b

0.94b

0.082

0.136

1

0.037

<0.001

2

1.28E 1.23E

1.19E 1.14EF

0.98bF 0.95bEF

1.01abF 0.90bF

1.02abF 0.86cF

0.067

0.005

3

1.22E

1.15EF

0.97bFG

0.92bG

1.00abFG

0.049

0.002

4

0.041

0.032

0.036

0.066

0.062

SEM

0.699

0.462

<0.001

0.011

0.009

p-value

abMean value in columns with different superscripts are significantly different (p<0.05) EFG Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different

3.1.2.4. Dry matter of urea treated cassava stems

Urea level had no effect on the DM content of the cassava stems during the first

two weeks of storage, when the DM content of the cassava stems did not change (Table

3.7); This result is similar to the report of Nguyen Xuan Trach et al. (2006), Dang Vu

Binh et al. (2007), they reported that use of urea to alkalize did not change DM of

straw. The authors said that there was no significant fermentation process in the

alkalization of agricultural by-products. But from 4 to 8 weeks of storage, the DM

content declined linearly, and the decline was increased linearly with the level of added

urea. The alkali process dissolves a number of soluble compounds and transforms into

a gas or liquid in the compost and is lost during the analysis.

Table 3.7. Effect of urea level and storage time on DM of cassava stems

23.6E

23.3abE

22.8abEF

20.8aFG

20.1aG

0.515

0.001

Storage time, weeks SEM p-value Urea (%) 0 2 4 6 8

23.2E

23.3abE

22.2abE

17.8bEF

18.5bF

0.557

<0.001

24.1E

22.0bE

23.3aEF

19.2abFG

19.7aG

0.593

<0.001

23.5E

24.6aE

22.4abE

17.7bcF

18.1bF

0.576

<0.001

23.7E

24.5 aE

17.2cG

0.347

<0.001

16.5cG

21.1bF

0.538

0.455

0.718

0.569

0.347

0.022

0.911

<0.001

0.001

SEM

p-value 0.046 abc Mean value in columns with different superscripts are significantly different (p<0.05) EFG Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different. 3.1.2.5. Crude protein (CP) content of treated cassava stems

The protein value of cassava also depends on many factors such as harvesting

time, cultivation techniques and seasonality (Tran Thi Hoan, 2012). In this experiment,

cassava stems were harvested from many different fields, growing stages and regions,

so this may be a factor affecting the protein value of the stems (Table 3.8). The

magnitude of the CP increase of treated cassava stems varies according to many factors

such as material, environment and procedure of the treatment process. Furthermore, the

CP increases are related to the urea level in the treatment, the water content of material,

and the temperature. Variation of material CP concentration determines the magnitude

of the increase, and higher increases were noted for cassava stems with low CP

concentration after urea treatment. The CP concentration of cassava stems was

increased significantly when treating with urea, with CP increases from 1.55 to 3.2%,

depending on level of urea (Dang Hoang Lam, 2013). In the present study an increase

of 1.4 to 2.5 times the CP content was found, depending on level of urea after 2 weeks

of storage. These results were similar to many studies on fresh rice straw in which the

CP increases were from 3.6 to 6.4 times that of untreated fresh rice straw CP

concentration (4.8% of DM) in the study of Chowdhury and Huque (1996a), 2.1 folds

in the untreated rice straw (6.88% of DM) in the study of Man and Wiktorsson (2001);

CP content in rice straw treated with urea was increased from 9.04 to 9.37% (Nguyen

Xuan Trach et al., 2006).

Table 3.8. Effect of urea level and storage time on crude protein in cassava stems

Storage time, weeks

SEM

p-value

Urea (%)

0

2

6

8

4

6.14 aE

6.11dEF

5.63dG

5.18eH

0.014

<0.001

6.06eF

0

8.48dE

8.0cEF

7.98dEF

0.147

0.009

7.69bF

8.43cE

1

9.74cE

9.71bE

9.40cF

0.065

<0.001

8.01cG

8.08cG

2

13.6bE

13.4aE

13.3bE

0.197

<0.001

8.41dF

13.7bE

3

14.0aG

0.172

<0.001

14.9aEF

14.2aFG

10.0eH

15.3aE

4

0.074

0.134

0.119

0.194

0.138

<0.001

SEM <0.001 p-value abcd Mean value in columns with different superscripts are significantly different (p<0.05) EFGH Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error of mean p- value: The level of statistical significance is different.

The data for crude protein (N*6.25) is misleading as they do not differentiate

between true protein and the products of multiplying the nitrogen content by 6.25. The

result of major concern for the farmer is the loss of DM from the combined effect of

storage time and level of added urea, which resulted in the DM content of the stored

stems declining from initial values of 23.6% to 17.6% after 8 weeks of storage with 4%

added urea (a loss of about 24%; Table 3.8)

3.1.2.6. NDF and ADF of cassava stems treated

The NDF (Table 3.9) and ADF (Table 3.10) were significantly affected by urea.

After the second week of storage, NDF and ADF levels were reduced linearly by

increasing 4 of 8 levels of urea and by length of storage time; however, the changes

were of relatively small order.

Both ADF and NDF of alkaline products between treatments and storing periods

were decrease significantly. Specifically, ADF of cassava stems treated was decreased

and significantly different between treatments (p = 0.003) and decreased significantly

after 4 weeks of storage (p= 0.001) from 3.4% (3% urea level) to 5.8% (4% urea level)

lower than fresh cassava stems; NDF of cassava stems was also decreased significantly

among treatments and different storing period (p<0.001). Particularly, NDF was

decreased with higher urea levels, and after 4 weeks of storage, almost of NDF was not

reduced significantly at 6th & 8th week storage. The mean of most treatments with high

levels of urea (3% and higher) had a strong ammonia smell and pH values higher than 8

that environment has just started to break down the lignin, cellulose and hemicellulose

bonds, and make a part of hemicellulose dissolved.

Table 3.9. Effect of urea level and storage time on NDF in cassava stems

Storage time, weeks

SEM

p- value

Urea (%)

2 64.5aEF

4 63.4aF

6 62.9aF

8 62.6aF

0.467

0.001

0 65.8E

0

61.6bF

60.7bFG

60.4bG

60.2bG

0.290

<0.001

65.8E

1

60.6bF

59.3bcGF

59.0bcG

58.9bcG

0.310

<0.001

65.8E

2

58.9cF

58.3cF

58.2cF

0.177

<0.001

65.2E

3

59.2cF

58.3cF

58.2cF

58.1cF

0.320

<0.001

65.3E

4

0.201

0.318

0.352

0.353

0.386

SEM

0.071

<0.001

p-value

abc Mean value in columns with different superscripts are significantly different (p<0.05) EFG Mean value in rows with different superscripts are significantly different (p<0.05) SEM: standard error mean p- value: The level of statistical significance is different.

These results are agreement with Trach (2000). Urea treatments have an effect on

cassava stems cell walls. The changes in NDF were mainly determined by treatment

effect on hemicellulose. It is probably becauses hemicellulose it most sensitive to

delignification treatment because hemicellulose polysaccharides are held in place by

cross-linkages to lignin and on delignification much of the hemicellulose become soluble

(Van Soest, 1994).

Table 3.10. Effect of urea level and storage time on ADF in cassava stems.

Storage time, weeks

Urea (%)

SEM

p-value

0

2

4

6

8

50.7

50.7a

50.2a

50.6a

0.444

0.900

0

50.8

50.9a

49.2a

49.1ab

49.3ab

0.384

0.007

1

50.5E

49.8abEF

48.5aF

48.9abF

48.6bF

0.315

0.002

2

50.1E

50.0abE

48.3aF

48.1bcF

46.9bG

0.169

<0.001

3

50.4E

48.6bF

46.5bG

46.6cG

45.4dG

0.382

<0.001

4

0.330

0.358

0.380

0.347

0.386

SEM

0.585

0.003

<0.001

p-value

preserved safely and with improved nutritional value by urea. The urea level at 3% and 4 %

was a good method for preserving and improving nutritive value. The nitrogen content was

dramatically increased in cassava stems treated with urea, but the amount of N in 4% urea

treated cassava stems would be too high and an expensive way of suppling the N, as the level is

required for effective treatment but much greater than what is needed by the rumen microbes.

Therefore, the best level of urea of 30g urea kg-1 DM cassava stems is good for improving

nutritive value and storing at least 8 weeks.

Based on these results it is concluded that alkaline cassava stems can be

The slight decline in the percentages of NDF (about 10%) and ADF (4%)

account for only part of the losses; the remainder supposedly being in the form of

soluble carbohydrates. There may have been some gain in true protein during storage,

but this could not be ascertained in the absence of analytical data for true protein.

3.2. EXPERIMENT 2

3.2.1. Composition of the diet ingredients

Urea-treatment of the cassava stems doubled the crude protein content (Table

3.11). The WRC (water retention capacity) of 4.6 liters of water per 1 kg of biochar

was similar to that reported for combustion of rice husks in a down-draft gasifier

(Orosco et al., 2018) and indicates that the biochar had a high “adsorptive” capacity.

Table 3.11. Chemical composition of diet ingredients (UCS is urea-treated cassava stems) in

experiment 2

% in DM

Items

DM, % CP ADF NDF OM

WRC

pH

33.4

5.50 51.8 66.3

93.5

UCS

23 .0

11.7 51.4 67.1

92.0

6.92

Water spinach

13.6

18.1 27.6 36.2

93.4

Biochar

90.4

4.60

Notes: nd: Not determined; WRC: Water retention capacity CS: cassava stems; UCS: urea treated cassava stems DM: Dry matter. CP: Crude protein; ADF: Acid detergent fiber; NDF: Neutral detergent fiber, OM: Organic matter 3.2.2. Feed intake and digestibility

There were differences in feed intake, apparent digestibility coefficients and N

retention due to addition of biochar (Table 3.12). biochar is believed to act by forming

a biofilm within the fermentation medium (Leng et al 2012a), there were carryover

effects the 14 days periods during which the biochar was fed or not fed. This were

shown that the potential benefits that have been shown to occur in feeding trial (Leng et

al 2012b).

There were major benefits from feeding water spinach along with the urea

treated cassava stems (Table 3.12). DM intake was increased 18% by supplementing

the urea-treated cassava stems with biochar which was fed separately (Figure 3.8) at

1% of the diet DM (Table 3.12; Figure 3.9). Addition of water spinach increased total

DM intake by 25% while the combined effect of biochar plus water spinach was to

increase intake by 41%.

Coefficients of apparent DM digestibility were increased more by biochar (by

9%) than by water spinach (2.4%) (Table 3.13; Figures 3.10 and 3.11). The combined

effect of biochar + water spinach was to increase DM digestibility by 12%. Results for

organic matter were similar. Digestibility coefficients for crude protein have no real

meaning when the major part of the dietary nitrogen (40-50%) is in the form of NPN

(urea and ammonia) derived from urea-treatment of the cassava stems.

Table 3.12. Effect of biochar and water spinach on feed intake

Treatment

Unit (gDM/day)

SEM

p- value

UCS

UCSB

UCSW

UCSWB

UCS

367a

300b

352ab

428a

15.10

0.002

Biochar

3.91

3.84

0.450

<0.001

Water spinach

159

163

3.306

<0.001

Total DM intake

367b

459ab

519a

432ab

19.97

0.009

DMI, % LW

2.27d

2.83b

3.12a

2.59c

0.048

<0.001

OMI (gDM/day)

337c

428ab

488a

391bc

15.04

<0.001

CP in DM, %

11.4b

14.05a

14.07a

11.6b

0.512

0.003

4.35

0.207

0.376

ME (MJ/kgDM)

4.00

4.12

4.47

abcd Mean value in rows with different superscripts are significantly different (p<0.05) UCS: urea treated cassava stems; UCSB: UCS with biochar; UCSW: UCS with water spinach; UCSWB: UCS with water spinach and biochar. SEM: standard error of the mean p- value: The level of statistical significance is different.

All these effects appear to have been caused by the increased crude protein

content of the diet when the water spinach was fed (13.0 versus 9.4% in the DM in

table 3.14). When the N retention data were corrected for differences in N intake the

effects of the water spinach were no longer apparent. These effects of increasing intake

of diet DM, and especially of the dietary concentration of crude protein, with resultant

improvements in N retention, are similar to those observed by Kongmanila et al. (2007)

when they supplemented Mango foliage with water spinach.

UCS

Biochar Water spinach

600

500

400

d / g

300

, e k a t n i

200

M D

100

UCS

UCSB

UCSW

UCSWB

Figure 3.9. Supplements of water spinach and biochar increased DM intake by goats fed urea-

treated cassava stems

Table 3.13. Effect of water spinach and biochar on nutrient digestibility (%) in goats fed urea

treated cassava stems

Treatment

SEM

p-value

Items (%)

UCSB

UCSW

UCSWB

UCS

Dry matter

64.8a

60.8b

66.3a

0.88

0.001

59.4b

Crude protein

60.1ab

61.7ab

63.1a

1.54

0.010

53.2b

Organic matter

65.0

61.6

66.8

1.78

0.066

59.4

ab, Means within rows without common superscripts differ at P<0.05 UCS: urea treated cassava stems; UCSB: UCS with biochar; UCSW: UCS with water spinach; UCSWB: UCS with water spinach and biochar. SEM: standard error of the mean p- value: The level of statistical significance is different.

No WS WS

NoBio

Biochar

, y t i l i

b i t s e g d M D

NoBio

Biochar

No WS

Biochar

Water spinach

Figure 3.10. Effect of water spinach on DM

Figure 3.11. Effect of biochar on DM

digestibility in goats fed urea-treated cassava

digestibility

in goats

fed urea-treated

stems with or without a supplement of biochar

cassava stems with or without a supplement

of water spinach

3.2.3. Nitrogen retention

The most dramatic effects of biochar supplementation were on N retention

(Table 3.14; Figures 3.12 and 3.13) and the biological value of the protein absorbed

(calculated as the N retained as percent of N digested) (Figures 3.14 and 3.15)

Table 3.14. Nitrogen balance in goats fed urea-treated cassava stems supplemented with or

without fresh water spinach and biochar.

Treatments

SEM

p-value

Items

N balance, g/d

Intake

UCS 8.13c

UCSB 9.36bc

UCSW 12.4ab

UCSWB 13.0a

0.782

0.001

Feces

3.79bc

3.65c

5.09a

4.81ab

0.245

0.003

Urine

1.30

1.17

1.42

1.25

0.217

0.874

Nitrogen retention

(g/day)

3.03b

4.42ab

5.84a

6.91a

0.607

0.004

% of N intake

37.4b

47.3ab

46.9ab

52.9a

2.55

0.008

% of N digested

69.9c

78.6b

80.0ab

84.4a

1.390

<0.001

Notes: a,b,c Mean values with the different letters in the same rows are significantly different at the level of P≤0.05 UCS: urea treated cassava stems; UCSB: UCS with biochar; UCSW: UCS with water spinach

Biochar increased daily N retention by 46.9% on the diet of urea-treated cassava

stems and by 21% when water spinach replaced half of the urea-treated cassava stems

(Table 3.14). Comparable values for the increases in the biological value of the protein

were 12.2 and 4.4%.

Biochar provides essentially no protein thus the increase in N retained and in its

biological value can only have come about as a result of the biochar stimulating rumen

microbial growth resulting in an increase in synthesis and hence of absorption of amino

acids. We postulate that biochar functions as a “prebiotic” – stimulating the activity of

beneficial microbial communities through its support for biofilms in the digestive tract

No water spinach

Water spinach

No biochar

Biochar

of the animal.

d

7 6

/ g

,

n o i t n e t e r N

8 7 6 5 4 3 2 1 0

No water spinach

Water spinach

No biochar

Biochar

Water spinach

Biochar

Figure 3.12. Effect of water spinach on N retention in goats fed urea-treated cassava stems with or without a supplement of biochar

Figure 3.13. Effect of biochar on N retention in goats fed urea-treated cassava stems with or without a supplement of water spinach

No water spinach

Water spinach

No biochar

Biochar

120.0

100.0

d e t s e g i

80.0

N d e t s e g i

d f o

60.0

%

N

d f o

,

40.0

%

40.0

,

20.0

0.0

n o i t n e t e r N

No water spinach Water spinach

No biochar

Biochar

n o i t n e t e r N

Figure 3.14. Effect of water spinach on N retention as % of digested N in goats fed urea- treated cassava stems with or without a supplement of biochar

Figure 3.15. Effect of biochar on N retention as % of digested N in goats fed urea-treated cassava stems with or without a supplement of water spinach

It is hypothesized that biochar promotes a habitat for micro-organisms that

detoxify phytotoxins (Leng, 2017); and that the “free” selection of biochar is an

example of “self-medication”, similar to that reported by Struhsaker et al. (1997).

These authors reported that: “charcoals absorb organic materials, such as phenolics,

particularly well and, as a consequence, remove these compounds, which have the

potential to be toxic or interfere with digestion or both”.

We suggest that biochar functions as a “prebiotic” – stimulating the activity of beneficial microbial communities through its support for biofilms in the digestive tract

that enhance the growth of microbiota that degrade phytotoxins and mycotoxins and increase the synthesis of essential amino acids from ammonia.

4. CONCLUSIONS

Based on the results of experiments in goats fed urea-treated cassava stems supplemented with or without fresh water spinach (1% of LW, DM basis) and biochar

at 1% of DM intake, we concluded:

level. Urea treated cassava stems were preserved safely up to 8 weeks and improved nutritive value. Urea treated cassava stems increased the crude protein (probably as

- The mixed level of urea at 3% DM basic with cassava stems was the best treatment

ammonia) from 5.5 to 11.7% in DM. The concentration of HCN decrease sharply after storage time.

- Dry matter intake was increased 18% by supplementing the urea-treated cassava stems with biochar. Supplementation with water spinach increased total DM intake by

25% while the combined effect of biochar plus water spinach was to increase intake by 41% compare to the control.

- Biochar increased daily N retention by 46.9% and the biological value of the

absorbed N by 12.2%.

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CHAPTER 4 EFFECT OF DIFFERENT LEVELS OF BREWERS’

GRAINS SUPLEMENTATION ON PERFORMANCE AND

METHANE EMISSION OF GOATS FED CASSAVA

FORAGE

Abstract

The present study objective provided further evidence for the prebiotic effect of

brewers’ grains in a basal diet of cassava forage fed to growing goats. The experiment

was carried out in An Giang University. Four “Bach Thao” goats (14 ± 2 kg) were fed

fresh cassava forage (sweet variety) ad libitum and 4 levels (0, 2, 4 and 6%, DM basis)

of brewers’ grains in a 4*4 Latin square changeover design with periods of 15 days.

Adding 4% of brewers’ grains to the diet of cassava forage increased the DM intake,

the apparent DM digestibility, the N retention and the biological value of the absorbed

nitrogenous compounds. The methane levels in eructed gas increased with a positive

curvilinear trend as the intake of brewers’ grains in the diet was increased. The benefits

of small quantities of brewers’ grains in the diet are believed to be related to their

“prebiotic” qualities in enhancing the action of beneficial microbial communities along

the digestive tract of the animal.

Key words: Bach Thao, biofilms, biological value, microbial communities, prebiotics,

1. INTRODUCTION

Cassava (Manihot esculenta Crantz) is a major crop in Vietnam, grown on

570,000 ha producing annually some 1 million tonnes of roots (GSO, 2016). The roots

are used mainly for manufacture of starch and as an ingredient in livestock feed.

Growing the crop as a semi-perennial forage with repeated harvesting at 2 to 3month

intervals is a recent development (Wanapat 1997; Preston and Rodriguez, 2004).

Several reports have shown the benefits of the fresh forage as a source of bypass

protein in ruminant diets based on molasses-urea (Ffoulkes and Preston, 1978), rice

straw (Do et al., 2002; fresh cassava stems (Trinh Xuan Thanh et al., 2013) and ensiled

cassava pulp-urea (Keopaseuth et al., 2017; Binh et al., 2017).

The use of fresh cassava forage as the sole diet of goats was pioneered by Sina

et al., 2017. Growth rates on a diet of fresh cassava forage were 65 g/day and were

more than doubled to 160 g/day when a small supplement (5%) of ensiled brewers’

grains was included in the diet, It was proposed that this “synergistic” effect of the

brewers’ grains was due to its role as a source of beta-glucan, a component of the cell

walls of cereal grains and fungi such as yeasts, that has been shown to have prebiotic

properties (Novak and Vetvicka 2008).

The present experiment was designed to provide further evidence for the prebiotic

effect of brewers’ grains in a basal diet of cassava forage fed to growing goats.

Proportions of ensiled brewers’ grains above (6%) and below (2%) the 4% level were

compared to identify the optimum level.

2. MATERIALS AND METHODS

2.1. EXPERIMENTAL DESIGN

The experiment was conducted from July to November 2016 at An Giang

University farm, An Giang province, Vietnam. Four “Bach Thao” goats (14 ± 2 kg) were

fed the 4 levels if ensiled brewers’ grains (0, 2, 4 and 6% DM basis) as the only

supplement to a diet of ad libitum fresh cassava forage (sweet variety). The design was a

Latin square (Table 4.1) with four treatments and four periods, each lasting 15 days (ten

days for adaptation and 5 days for collection of feces and urine). Between each period

there was a period of 7 days for resting during which time they were fed cassava forage

and the level of brewers’ grain designated for the subsequent period of the experiment.

Table 4.1. The layout of the experiment

Period

Goat 1

Goat 2

Goat 3

Goat 4

BG0

BG4

BG6

BG2

BG6

BG2

BG0

BG4

BG0

BG2

BG6

BG2

BG6

BG4

BG0

Notes: BG0, BG2; BG4; BG6: Treatments supplemented

brewers’grain levels of 0, 2, 4, 6% (DM basic)

2.2. ANIMALS AND MANAGEMENT

The goats were housed in metabolism cages made from bamboo, designed to

collect separately feces and urine. They were vaccinated against Pasteurellosis and

Foot and Mouth disease and treated with Ivermectin (1ml/10 kg live weight) to control

internal and external parasites. They were weighed between 06:30 and 07:30h before

feeding at the start and end of each experimental period.

2.3. FEEDS AND FEEDING

The cassava (sweet cassava variety) was planted in sandy soil in the An Giang

University farm. from April to October 2016. It was fertilized with 8 tonnes/ha of cattle

manure, 175kg urea, 200 kg Super-phosphate and 130kg potassium chloride. The first

application was between 25 and 30 days after planting and the second application from

50 to 60 days after planting.

The forage was harvested 50-60cm above soil level at intervals of 120 days

when it had attained a height of 100 - 120 cm. Harvesting of the cassava was done 2h

prior to each feed, morning and afternoon. The forage was chopped by hand prior to

being put into the feed troughs. The brewers’ grains were brought from Kien Giang

province every 5 days. They were stored in closed plastic bags. The chosen amounts

were offered twice daily in troughs separate from the cassava forage. Feed refusals

were weighed every morning prior to giving the new feed. Samples of each diet

component were collected daily and bulked at the end of each period for analysis.

2.4. DIGESTIBILITY AND N RETENTION

During the data collection periods, the feces and urine were recorded twice

daily at 7:00 and 16:00 and added to jars containing 100 ml of 10% sulphuric acid. The

pH was measured and, if necessary, more acid added to keep the pH below 4.0.

After each collection period: (i) a sample of 10% of the urine was stored at -4o C for

analysis of nitrogen (AOAC 1990); (ii) the feces were mixed and a sample (10%)

stored frozen at -20oC.

2.5. RUMEN PARAMETERS

Rumen fluid was taken by stomach tube 3h after the morning feed following the

last day of each collection period. During this time the goats were still on the

designated diet for that period. The pH of the fresh fluid was determined by using an

electronic meter (Eco Testr pH2. The protozoan population in the rumen fluid was

estimated by diluting 8 ml of ruminal fluid with 16 ml of formaldehyde-saline solution

(37 % formaldehyde with saline solution 1:9) and counting the protozoa under light-

microscopy (100x magnification) using a 0.2 mm deep Dollfus counting chamber. Four

fields in the counting chamber were filled and protozoa counted, according to the

method described by Jouany and Senaud (1979) and Dehority (1993)

2.6. RUMEN GAS EMISSIONS

At the end of each period the goats were confined individually in a gas-proof

chamber (a bamboo frame covered with polyethylene plastic) for sampling of eructed

gases and residual air in the chamber. Measurements of the concentrations of methane

and carbon dioxide were taken continuously over a 10-minute period, using a Gasmet

infra-red meter (GASMET 4030; Gasmet Technologies Oy, Pulttitie 8A, FI-00880

Helsinki, Finland).

2.7. ANALYTICAL PROCEDURES

The sub-samples of feeds offered and refused, and of the feces, were analysed

for dry matter, ash and nitrogen by AOAC (1990) methods. Neutral detergent fiber

(NDF) and acid detergent fiber (ADF) were analyzed according to the procedure of

Van Soest and Robertson (1991). Nitrogen in urine and ammonia in rumen fluid were

determined by the Kjeldahl method (AOAC 1990). Metabolizable energy (ME) of the

diet (MJ/kg) were calculated from organic matter digestibility (OMD: %) by formula of

Mc Donald et al. (2002). The formula is: ME = 0.160*OMD.

2.8. STATISTICAL ANALYSIS

Data were analyzed with the General Linear Model option of the ANOVA

program in the MINITAB software (Minitab 2016). Sources of variation were

treatments, animals, periods and error.

3. RESULTS AND DISCUSSION

3.1. COMPOSITION OF DIET INGREDIENTS

The crude protein (CP) of the cassava forage (leaf and petiole combined) was

considerably lower than the value of 21% CP in DM reported by Sina et al., 2017

where the leaf alone had 29% CP in DM and the petiole 9.6% in DM.

Table 4.2. Composition of diet ingredients

% in DM

DM, %

CP

NDF

ADF Ash

pH

21.9

12.6

47.0

39.1

7.77

Cassava forage

23.7

26.4

36.8

26.6

5.37

4.35

Brewers’ grains

Notes: DM: Dry matter, CP: cruduce protein, NDF: Neutral Detergent fiber; ADF:

Acid detergent fiber

3.2. FEED INTAKE AND DIGESTIBILITY

DM intake followed a curvilinear trend with the peak intake occurring when the

BG content of the diet DM reached 4%, declining when the BG was raised to 6%

(Table 4.3 and Figure 4.1).

Table 4.3. Feed intake in goats fed cassava forage supplemented with different levels of

brewers’ grains

Treatment

SEM

p-value

Items

BG0

BG2

BG4

BG6

DM intake, g/d

Cassava forage

441c

486b

540a

468b

5.92

<0.001

Brewers’ grains

0.00d

10.7c

22.3b

30.7a

0.09

<0.001

Total DM

441c

497b

562a

498b

6.33

<0.001

% of DM intake

Brewers’ grains

0.00

2.15

3.97

6.16

0.05

<0.001

Crude protein

12.9

14.0

13.5

14.6

0.54

0.192

ME (MJ/day)

3.55b

3.90ab 3.80ab

4.45ab

0.189

0.034

Notes: BG0; BG2; BG4 and BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic) abcd Mean values with different letters within the same rows are significantly different at the level of P≤0.05

700

600

500

y a d / g

400

y = -0.3137x2 + 12.067x + 430.25 R² = 0.6238

300

, e k a t n i

M D

200

100

0 0.00

5.00

10.00

30.00

35.00

40.00

25.00 20.00 15.00 Brewers' grain, g/day

Figure 4.1. Relationship between dry matter inatke and different level of brewers’

grain in goats fed cassava forage.

These results are in agreement with Do et al. (2002), increasing the proportion

of cassava forage DM fed to goats from 0 to 47% of total DM feed offered resulted in

increased DM intake (DMI), organic matter (OM) digestibility and nitrogen retention.

Another author as Sokerya & Rodriguez (2001) found that the growth rate of goats was

higher when a diet based on brewer’s grain was supplied with cassava.

According to Nguyen Van Thu (2016) brewery grain is an energy sources as

well as a source of proteins. In the present results, metabolizable energy was increased

by the level of brewers’ grains in the diet. The level of CP in the treatment 3 was 7,5g

CP/kg LW/day with the ME intake and daily gain of 3.80 MJ/day and 142g,

respectively. This result is the same of results in Nguyen Duy Khanh (2015) who

concluded that for Bach Thao goats from 10 to 15 kgLW the optimum level of CP in

the diet is 7g CP/kg LW/day with an ME and daily weight gain of 3.86 MJ/day and

120g, respectively.

Table 4.4. Nutrient digestibility (%) in goats fed cassava forage supplemented with

different levels of brewers’ grains

Treatments

SEM

p-value

Items

BG0

BG2

BG4

BG6

62.4a

69.9b

72.7b

70.8b

1.66

0.021

55.9a

67.2b

70.8b

65.5b

2.7

0.036

53.0a

58.2b

66.0c

56.6ab

1.05

0.001

NDF

57.8

67.4

70.6

63.0

4.34

0.248

Notes: CP: crude protein; DM: dry matter; OM: organic matter, NDF: neutral detergent fiber; BG0, BG2; BG4; BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic). abc Mean values with the different letters in the same rows are significantly different at the level of P≤0.05

Crude protein

y = -0.5106x2 + 4.5607x + 62.408 R² = 0.6694

y = -0.9023x2 + 7.2186x + 55.866 R² = 0.6421

y t i l i b i t s e g i d t n e r a p p A

5 2 Brewers' grain, % in diet DM

Figure 4.2. Correlation between the differnce level of brewers’ grains and apparent

digestibility of DM and CP

3.3. RUMEN PARAMETERS

All criteria of rumen fermentation showed that linear decreasing trends as the

level of brewers’ grains in the diet was increased (Table 4.5; Figures 4.3). The probable

explanation of this trend is that appetite and therefore rumen fermentation, are

stimulated following the offering of the fresh ensiled brewers’ grains in the morning.

Reduction in ammonia levels and protozoan numbers are the logical result of the

decrease in pH due to the increased rate of fermentation at the time of measurement.

Table 4.5. Protozoa numbers, ammonia and pH in rumen fluid, before and 4h after, offering

fresh feed in the morning

Treatments

SEM

p-value

Items

BG0

BG2

BG4

BG6

Before feeding

Protozoa, x10-5/ml

14.1

13.1

12.8

12.7

0.388

0.098

129

123

112

113

4.640

0.059

NH3, mg/liter

7.35

7.21

7.35

0.081

0.557

4h after feeding

Protozoa, x10-5/ml

15.8a

14.6ab

13.8b

13.3b

0.459

0.020

127a

114ab

111ab

95.9b

7.261

0.009

NH3, mg/liter

6.94a

6.85a

6.60b

6.34c

0.056

<0.001

Notes: BG0, BG2; BG4; BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic) abcMean values with the different letters in the same rows are significantly different at the level of P≤0.05 SEM: standard error of the mean p- value: The level of statistical significance is different

Before 4h after

160

y = -2.962x + 128.37 R² = 0.3874

140

120

r e t i l / g m

100

y = -5.1235x + 128.73 R² = 0.6321

, a i n o m m a

n e m u R

4 Brewers' grains, % in diet DM

Figure 4.3. Relationship between different levels of brewers’ grains and rumen

ammonia before and after offering new morning feed.

3.4. NITROGEN RETENTION

Retention of nitrogen, per day and as a percentage of the nitrogen digested,

showed curvilinear trends with the optimum coinciding with the 4% level of brewers’

grains in the diet (Table 4.6; Figures 4.4). The effect of adding 4% brewers’ grains to

the diet was a 65% increase in N retention and a 14% increase in N retained per unit of

N digested.

Table 4.6: N balance (g/day) in goats fed cassava forage supplemented with different

levels of brewers’ grain

Treatments

Nitrogen

SEM

p-value

BG0

BG2

BG4

BG6

Nitrogen balance, g/d

Intake

9.82

11.1

12.1

11.6

0.836

0.291

Feces

3.75

3.36

3.35

3.49

0.480

0.491

Urine

1.63a

1.27b

1.49ab

1.64a

0.066

0.024

Nitrogen retention

g/d

4.44b

6.48a

7.27a

6.51a

0.286

0.007

% of N intake

45.6

58.4

60.2

56.0

4.55

0.070

% of N digested

72.6b

83.5a

82.8a

79.8a

1.66

0.002

Notes: BG0, BG2; BG4; BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic) ab Mean values with the different letters in the same rows are significantly different at the level of P≤0.05 SEM: standard error of the mean p- value: The level of statistical significance is different

100

d e t s e g i D N

y = -0.7959x2 + 5.9608x + 72.995 R² = 0.7363

f o %

n o i t n e t e r

5 2 Brewers' grain, % in diet DM

Figure 4.4. Relationship beween of dietary level of brewers’ grains and N

retention as a percentage of N digested

The 65% increase in N retention, and corresponding increase in live weight

gain, with addition of 4% brewers’ grains to an exclusive diet of fresh cassava forage,

followed by the decline in N retention when the proportion of brewers’ grains was

increased to 6%, shows that the benefit of the brewers’ grains was not only by

enhancing the supply of bypass protein. On the other hand, the 14% increase in N

retention as percentage of digested nitrogen indicates that the biological value of the

absorbed amino-acids was improved by supplementation with brewers’ grains, the

implication being that the brewers’ grains had facilitated the activity of rumen microbes

in the synthesis of microbial protein. We suggest that these results strengthen the

original proposal of Binh et al. (2017) “that the brewers’ grains act as a site

(substratum) for biofilm attachment of detoxifying microbes and as a source of

nutrients for their detoxifying activity”. In this respect, the benefits of the small

quantity of brewers’ grains in the animals’ diet suggest that in this context their role is

as a “prebiotic” enhancing the activities and effectiveness of beneficial microbial

communities.

3.5. LIVE WEIGHT GAIN AND FEED EFFICIENCY

Live weight and feed efficiency followed a curvilinear trend with the peak

intake occurring when the BG content of the diet DM reached 4%, declining when the

BG was raised to 6% (Table 4.7 and Figure 4.5 &4.6).

Table 4.7. Live weight gain and feed efficiency in goats fed cassava forage

supplemented with different levels of brewers’ grain

Treatments

Items

SEM

p-value

BG0

BG2

BG4

BG6

Live weight, kg

Initial

15.0

14.0

15.5

15.1

Final

20.7

22.1

20.4

18.0

Daily gain, g/day

96.7b

142c

80.0b

48.3a

10.4

<0.001

DM inatake, g/day

497b

562a

498b

441c

6.33

<0.001

DM Feed efficiency

0.11b

0.20ab

0.25a

0.17ab

0.026

0.016

Notes: DM: dry matter; BG0, BG2; BG4; BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic) abc Mean values with the different letters in the same rows are significantly different at the level of P≤0.05

180

160

y = -6.4795x2 + 46.675x + 43.143 R² = 0.765

140

120

y a d / g

100

n i a g W L

0.0

1.0

3.0

4.0

6.0

7.0

2.0 5.0 Brewers' grain, % in diet DM

Figure 4.5. Relationship between live weight gain and different levels of brewers’ grain in goats fed cassava forage.

0.30

0.25

0.20

0.15

y = -0.0108x2 + 0.0766x + 0.1052 R² = 0.6696

0.10

y c n e i c i f f e d e e F M D

0.05

0.00

0.0

1.0

3.0

4.0

6.0

7.0

5.0 2.0 Brewers' grain, % in diet DM

Figure 4.6. Effect of level of brewers’ grains on DM feed efficiency

Coefficients of apparent digestibility of crude protein and DM showed the same

curvilinear trends as were recorded for DM intake, LW gain and feed efficiency, with

maximum values when the ensiled brewers’ grains were approximately 4% of the diet

DM (Table 4.7 and Figure 4.5 & 4.6). These results are similar to those of Vor Sina et

al. (2017), the positive effects of a small supplement of brewers’ grains (5-6% of diet

DM) on feed intake, growth and feed conversion of goats fed cassava foliage, are also

similar to those reported in cattle by Binh et al (2017). The reason for live weight gains

is the beneficial effect of the brewers’ grains in reducing the degree of toxicity of the

cyanogenic glucosides present in cassava forage. The lower concentration of

cyanogenic glucosides in the forage of sweet cassava varieties would have been offset

by the higher level of cassava forage (96-100% of the diet) in the present experiment.

3.6. METHANE EMISSIONS

The ratio of methane to carbon dioxide in the mixture of eructed gas and air in

the plastic-enclosed chambers increased with a curvilinear trend as the daily intake of

brewers’ grains was increased (Table 4.8; Figure 4.7). The trend was similar to that

reported when brewers’ grains replaced cassava forage in a fattening diet fed to cattle

(Binh et al., 2017: Keopaseuth et al., 2017); However, the replacement rate in both

these cases was over a much wider range of brewers’ grains, the proportion of cassava

forage was lower than and the basis of the diet was ensiled cassava pulp-urea.

Table 4.8. Mean values for the ratio methane: carbon dioxide in mixed eructed gas and air in

the plastic-enclosed chambers where the goats were enclosed over ten minutes periods

Treatments

SEM

p-value

BG0

BG2

BG4

BG6

0.026b

0.027b

0.031ab

0.042a

0.003

0.013

CH4/CO2

Notes: BG0, BG2; BG4; BG6: Treatments supplemented brewers’grain levels of 0, 2, 4, 6% (DM basic) ab, Means within rows without common superscripts differ at P<0.05

y = 0.0005x2 - 0.0004x + 0.0251 R² = 0.8684

o i t a R 2 O C : 4 H C

0.050 0.045 0.040 0.035 0.030 0.025 0.020 0.015 0.010 0.005 0.000

0.00

2.00

6.00

8.00

4.00 Brewers' grain, % in DM

Figure 4.7. Effect of increasing intake of brewers’ grains on the methane: carbon dioxide

ratio in mixed air-expired breath of the goats fed a basal diet of fresh cassava forage.

The inverse relationship between the propionic acid concentration in the rumen

fermentation and the proportion of methane in rumen gas has been observed in many

experiments (Syahniara et al., 2016). It is in line with the understanding that hydrogen

produced in fermentation is directed into propionate production and this will supply,

following it being absorbed, a source for glucose synthesis, which in ruminants appears

to be an essential nutrient. This may spare the degradation of absorbed amino acids for

this purpose where glucose requirements are high (late pregnancy, lactation and fast

growth) (Preston and Leng, 1987). Thus, the change in propionate has two benefits: it

preserves a greater proportion of the metabolisable energy and provides an essential

nutrient. The mechanism by which small quantities of brewers’ grain (4% of diet DM)

bring about these positive effects, benefitting animal performance, but increasing ratio

of methane and carbon dioxide is still to be identified. Here we suggest the idea that

substances in brewery grains (perhaps β-glucan or related compounds) support biofilm

formation which in turn increases the efficiency of microbial growth (Leng, 2014).

We have no explanation for the positive curvilinear relationship between daily

intake of brewers’ grains and the methane: carbon dioxide ratio in mixed eructed gas and

air when the goats were held for 10 minutes in the enclosed plastic-covered chambers.

4. CONCLUSIONS

Brewers’ grain is a high protein sources, which when used in small amounts as

supplementation for goats, has benefits and efficiency. Given the data in the present

study, it is concluded:

Adding 4% of brewers’ grains to a diet of cassava forage increased the DM

intake, the apparent DM digestibility, the N retention and the biological value of the

absorbed nitrogenous compounds.

The ratio of methane to carbon dioxide in the mixture of cructed gas increased

with a curvilinear trend as the level of brewers’ grains in the diet was increased.

The benefits of such small quantities of brewers’ grains are believed to be

related to their “prebiotic” qualities in enhancing the action of beneficial microbial

communities along the digestive tract of the animal.

REFERENCES

AOAC, 1990. (Association of Analytical Chemists) Official methods of Analysis. 15th edition. AOAC Inc, Arlington, Virginia, USA.

Binh P L T, Preston T R, Duong K N and Leng R A., 2017. A low concentration (4% in diet dry matter) of brewers’ grains improves the growth rate and reduces thiocyanate excretion of cattle fed cassava pulp-urea and “bitter” cassava forage. Livestock Research for Rural Development. Volume 29, Article #104.

Dehority B A., 1993. Laboratory manual for classification and morphology of ruminal ciliate protozoa, Boca Raton, FL, United States. CRC Press

roughage

Ffoulkes D. and Preston T. R., 1978. Cassava or sweet potato forage as combined in molasses-based diets: effect of sources of protein and supplementation with soybean meal. Tropical Animal Production. 1978. Volume3, Number 3.

Leng R A., 2014. Interactions between microbial consortia in biofilms: a paradigm shift in rumen microbial ecology and enteric methane mitigation. Animal Production Science 54, 519–543

Jouany J. P. and Senaud J., 1979. Role of rumen protozoa in the digestion of food cellulosic materials. Annales de Recherches Veterinaires, 10 (2-3): 261 - 263.

Keopaseuth T., Preston T. R. and Tham H. T., 2017. Cassava (Manihot esculenta Cranz) forage replacing brewer’s grains as protein supplement for Yellow cattle fed cassava pulp-urea and rice straw; effects on growth, feed conversion and methane emissions. Livestock Research for Rural Development. Volume 29, Article #35.

Minitab, 2016. Minitab Software. Release 16.0

Novak M. and Vetvicka V., 2008. Beta-glucans, history and action. and mechanisms of the present: Journal of aspects Immunomodulatory Immunotoxicology; 5: 47-57

Nguyen Duy Khanh, 2015. Effects of crude protein levels on feed intake, digestibility and growth of Bach Thao goat from 3-5 months of age. B.Sc. Thesis. Can Tho University. Vietnam.

Nguyen Van Thu, 2016. Recent Research and Development of Dairy Goat Production in Vietnam. In proceedings of 3rd Asian Autralian dairy goat. China. Pp.129-139

San Thy and Preston T. R., 2001. Potential of cassava in integrated farming systems. Livestock Research for Rural Development.

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Syahniara T. M., Ridlac M., Samsudind A. A. A B and Jayanegarac A., 2016. Glycerol as an energy source for ruminants: a meta-analysis of in vitro experiments. Media Peternakan, 39(3):189-194

Preston T R. and Leng R.A., 1987. Matching Livestock Systems to Available Resources in the Tropics and Subtropics. Penambul Books, Australia.

Preston T R. and Rodríguez Lylian, 2004. Production and utilization of cassava forage for livestock in integrated farming systems. Livestock Research for Rural Development. Volume 16, Art. No. 28.

Thomas D. and Schutze-Kraft R.,1990. Evaluation of five shrubby legumes in comparision with Centrosema acutifolium, Carimagua, Colombia. Tropical grassland 24: 87-92.

Thang et al., 2010. Effect of feeding cassava and/or Stylosanthes forage on the performance of crossbred growing cattle. Tropical Animal Health and Production 42(1) 1-11.

Toum K, Preston T. R. and Thâm Hô Tham, 2017. Cassava (Manihot esculenta Cranz) forage replacing brewer’s grains as protein supplement for Yellow cattle fed cassava pulp-urea and rice straw; effects on growth, feed conversion and methane emissions. Livestock Research for Rural Development. Volume 29, Article #35.

Tien Dung N., Thi Mui N. and Ledin I., 2005. Effect of replacing a commercial concentrate with cassava hay (Manihot esculenta Crantz) on the performance of growing goats. Animal Feed Science and Technology, 119(3-4), 271–281.

Thanh T.X., Hue K.T, Anh N.N. and Preston T R, 2013. Comparison of different forages as supplements to a basal diet of chopped cassava stems for growing goats. Livestock Research for Rural Development. Volume 25, Article #7

Van Soast J.B. Robertson and Lewis B.A., 1991. Methods for Dietary fiber, Neutral detergent fiber and nonstarch polysaccharides in relation to animal nutrition. A laboratory manual for animal science, Department of animal Science and Division of nutritional sciences, 613 Cornell University, Ithaca, New York.

Vanthong Phengvichith and Ledin I., 2007. Effects of supplementing gamba grass (Andropogon gayanus) with cassava (Manihot esculenta Crantz) hay and cassava root chips on feed Intake, digestibility and growth in goats. Asian-Australia Journal Animal Sciences. 20 (5): 725

Vor Sina, Preston T. R. and Thâm H.T., 2017. Brewers’ grains have a synergistic effect on growth rate of goats fed fresh cassava forage (Manihot esculentaCrantz) as basal diet. Livestock Research for Rural Development. Volume 29, Article #137.

Wanapat M, Pimpa O, Petlum A and Boontao U., 1997. Cassava hay: A new strategic feed for ruminants during the dry season. Livestock Research for Rural Development. Volume 9, Article #18.

101

CHAPTER 5 EFFECT OF BIOCHAR SUPPLEMENTATION LEVELS

ON GROWTH AND METHANE EMISSIONS OF GOATS

FED FRESH CASSAVA FORAGE

Abstract

An experiment was conducted in An Giang, Vietnam to test the hypothesis that

supplementation with biochar 0; 0.5; 1 and 1.5 % diet (DM based) would linearly

increase live weight gain and reduce methane emission of goat fed based cassava

forage. Twelve growing male goats of the Bach Thao breed, with an average initial

body weight 16 ± 1 kg, were housed in individual cages and given a basal diet of ad

libitum fresh cassava forage (sweet variety) supplemented with 4% (DM basis) of

ensiled brewers’ grain. The length of the trial was 12 weeks after a period of 10 days to

accustom the goats to the diets. For all the growth criteria (feed intake, live weight gain

and feed conversion), expected to be influenced by nutrient manipulation of ruminant

diets the responses were curvilinear with positive effects from increasing biochar

supplementation from 0 to 0.8% of the diet DM followed by a decline as the biochar

level was raised to 1.3% in diet DM. By contrast, in terms of effects on the rumen

fermentation the improvement (decrease in methane production) was linear. It is

hypothesized that the beneficial effects of biochar on growth of goats and cattle fed

cassava products is because the biochar provides habitat for microbial communities that

reduce the toxic effects of the HCN while still retaining its beneficial effects in

modifying the sites of digestion with positive effects on growth and feed conversion.

Key word: Biochar, goats, liveweight gain, cassava forage, methane emission.

1. INTRODUCTION

The population of goats in An Giang in 2017 was 6 times higher than in 2012

(Statistic yearbook of An Giang 2017). The relative price of meat from goats is higher

than that from cattle, eg: price of goat meat 3.2 USD/kg LW compared to cattle (2.5

USD/kg LW) (Do Thi Thanh Van et al., 2018). Most goats are kept in confinement in

small scale systems with the feed supplied from around the household or close by (eg:

natural grasses, water spinach, sweet potato leaves…but not cassava forage, that is

traditionally thrown away, or burned, causing environment pollution). This contrasts

102

with the report of Preston (2001), that cassava forage can be a valuable source of

protein for feeding to many kinds of animals. Brewers’ grains are the solid residue left

after the distillation of germinated cereal grains to produce beer and other alcoholic

beverages. The recent reports of benefits in growth and health of cattle and goats fed

small quantities of brewers’ grains (Thuy Hang et al 2018; Silivong et al 2018; Binh et

al 2017) are believed to be related to their “prebiotic” qualities in enhancing the action

of beneficial microbial communities along the digestive tract of the animal (Inthapanya

et al 2019). Biochar is generated from the partial combustion or fibrous biomass, and

although primarily used as a soil amendment (Lehmann and Joseph 2009; Preston

2015), it has recently been reported that at a level of 1% of the diet DM enhanced the

growth rate and reduced enteric methane emissions of cattle (Leng et al 2012) and goats

(Binh et al 2018; Silivong et al 2018).

The hypothesis underlying the research reported in this paper was that growth rate

and methane emissions of goats would reflect a dose response relationship to biochar,

which merited the study of levels of biochar in the range of 0 to 1.5% in diet DM.

2. MATERIALS AND METHODS

2.1. LOCATION AND DURATION

The experiment was carried out in the farm of the Faculty of Agricultural and

Natural Resources, An Giang University, An Giang Province, Vietnam, from February

2018 to May 2018.

2.2. EXPERIMENTAL DESIGN

Twelve growing male goats of the Bach Thao breed, with an initial body weight

16 ± 1 kg and about 3.5 – 4.5 months of age, were housed in individual cages (Figure1)

and given a basal diet of fresh cassava forage ad libitum plus 4% (DM basis) of ensiled

brewers’ grain. Treatments were 4 levels of biochar: 0, 0.5, 1.0 and .1.5% of diet DM.

The design was a randomized completely block design with three replicates of the four

treatments. The trial was for 12 weeks after a period of 15 days to accustom the goats to

the diets.

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Figure 5.1. The elevated cages for the goat

2.3. FEEDING AND MANAGEMENT

Cassava forage (sweet variety) was planted in An Giang University area. The

forage (leaves, petioles and stems) were harvested at 60 days intervals. The cassava

forage was fed to animals 2- 3 hours after harvesting. During rainy days, the forage was

harvested the day before feeding to limit the effects of excessive moisture on the forage

DM content. Harvesting was by hand-cutting the cassava stems at ground level then

rejecting the lower 50cm of “hard” stems (Figure 5.2). The forage was presented to the

goats by hanging it in bunches in front of the feed troughs.

Figure 5.2. The rest of the plant (red line on the

right) was suspended in the pens for the goats to

choose freely. The “hard” stems 40-50cm from

the ground was rejected.

The brewers’ grains were brought from the brewery in Kien Giang Province

every 10 days. They were stored in closed plastic bags in a naturally ensiled state (pH

4.28 ± 0.46). Each animal was offered a ration based on its DM intake in the previous

104

24 hours. The chosen amounts were offered twice daily in troughs. The biochar was

produced by burning rice husks in a top-lit, updraft (TLUD) gasifier stove (Olivier

2010). To reduce the “dusty” nature of the biochar it was mixed with a small amount of

water enough to moisten the biochar but avoiding any excess. The chosen amounts

were offered twice daily in troughs separate from the brewers’ grain (Figure 5.3). The

animals had free access to clean water for drinking.

Figure 5.3. Separate troughs for the brewers’ grains and the biochar

Before starting the experiment, the goats were treated against parasites with

injections of Ivermectin solution (1 ml per 4 kg LW) and vaccinated against

pasteurellosis, enterotoxaemia, foot and mouth disease and goat pox. They were adapted

to the experimental feeds for 15 days before starting the collection of data. Cassava

forage was fed at 7:30 and 14:30, while the brewers’ grain and biochar were given at

9:30 and 16:30. Mineral lick blocks (460 g limestone meal, 220 g bone meal, 50 g

sulphur, 100 g salt plus 170 g cement as a binding agent) were available ad libitum by

hanging on the walls of the pens. Feeds offered and refused were recorded daily.

2.4. MEASUREMENTS

Live weight was recorded in the morning before feeding at the beginning and at

10-day intervals until the end of the 90-day experiment. Live weight gain was

calculated from the linear regression of live weight (Y) on days from the start of the

experiment (X).

Feed consumption was recorded by weighing feeds offered and refusals from

individual animals every morning before offering new feed. Cassava forage (offered

and residues) was separated into stems and leaves (containing attached petioles) (Figure

5.4). Representative samples of each component were stored until they were analyzed.

105

Figure 5.4. Collecting samples of residues of the cassava forage

2.5. ERUCTED GAS EMISSIONS AND ANALYSIS

At the end of the experiment the goats were confined individually in a closed

chamber (a wood frame covered with clear glass) for sampling of eructed gases and

residual air in the chamber (Madsen et al 2010). Measurements of the concentrations of

methane and carbon dioxide were taken continuously over a 10-minute period, using a

Gasmet infra-red meter (GASMET 4030; Gasmet Technologies Oy, Pulttitie 8A, FI-

00880 Helsinki, Finland).

2.6. ANALYTICAL PROCEDURES

Samples of feed offered and refused were analysed for DM, crude protein (CP)

and ash by AOAC (1990) methods. Neutral detergent fiber (NDF), acid detergent fiber

(ADF) were determined by the methods of Van Soest et al. (1991). The equivalent

hydrogen cyanic acid content (HCN) in forage of fresh cassava leaves was determined

as per AOAC (2016). Condensed tannins were determined by the method of AOAC

955.35 (2016). The water retention capacity (WRC) of the biochar was determined by

suspending 100g (Wi) of dry biochar in 1 liter of water for 24h, after which it was

filtered, and the wet weight of biochar determined as Wf. The water retention capacity

was determined as: WRC = [Wf-Wi)]/Wi

2.7. STATISTICAL ANALYSIS

Data were analyzed with the General Linear Model option of the ANOVA

program in the MINITAB software (Minitab 2016). Sources of variation were

treatments and error. Production responses (feed intake, live weight gain and feed

conversion) were related to percent biochar in the diet using polynomial regression

equations from Microsoft Office Excel software.

106

3. RESULTS AND DISCUSSION

3.1. COMPOSITION OF DIET INGREDIENTS

The levels of crude protein in the cassava forage and combined leaf-petioles

(Table 5.1) were similar to those reported by Sina et al. (2017). The “equivalent HCN”

values in the forage (115 mg/kg DM) were much less than the 500 mg/kg DM reported

by Phuong et al. (2019) for leaf-petioles in sweet cassava.

Two batches of biochar were used in the experiment. The first batch, which was

fed during the 15-day adaptation period and the first 10 days of the growth trial had a

water retention capacity of 3.81 ml water/g dry biochar. The second batch which was

fed from day 10 of the feeding trial to the end after 90 days had a much higher water

retention capacity of 4.89.

Table 5.1. Composition of diet ingredients

% in DM

HCN WRC

DM, %

CP

Ash

ADF

NDF Tannin ppm ml/g

Cassava

2.99

115

28.1

13.7

6.8

39.2

48.3

Forage

26.8

5.4

10.9

41.2

51.4

cassava stems

29.4

22.1

2.7

37.3

45.1

Leaf + petiole

28.1

29.5

5.4

26.6

40.1

Brewers’ grain

89.6

76.9

3.81

Biochar (1)

95.7

69.7

4.89

Biochar (2)

Notes: DM: Dry matter, CP: Crude protein; ADF: Acid detergent fiber; NDF: Neutral

detergent fiber; HCN: Hydrogen cyanic acid; WRC: Water retention capacity.

3.2. FEED INTAKE

For all the growth criteria expected to be influenced by nutrient manipulation of

ruminant diets the responses were curvilinear with positive effects from increasing

biochar supplementation from 0 to 0.86% of the diet DM followed by a decline as the

biochar level was raised to 1.3% in diet DM (Table 5.2; Figures 5.5).

107

Table 5.2. Feed intake in goats fed increasing levels of biochar in a diet of fresh

cassava forage

Biochar, % in diet DM

DM intake (g/day)

SEM

p-value

B0

B0.5

B1.0

B1.5

Cassava forage

544b

560ab

623a

572ab

18.2

0.016

Brewers' grains

19.5

20.0

22.5

21.4

0.88

0.070

Biochar

2.11c

5.58b

7.74a

0.265

<0.001

Total

564b

582ab

652a

601ab

19.2

0.010

14.2

14.1

14.0

0.075

1.00

CP, % in DM

Notes: B0; B0.5; B1.0; B1.5: Treatments supplemented biochar levels of 0;0.5; 1.0; 1.5 (% in diet DM) acdb Means without common superscript differ at p<0.05 SEM: Standard error of the mean p-value: The level of statistical significance is different

800

700

600

d / g

500

y = -120x2 + 199x + 551 R² = 0.52

, e k a t n i

400

M D

300

200

100

0.2

0.4

0.6

0.8

1.2

1.4

Biochar, % in DM

Figure 5.5. Curvilinear response of DM intake of goats to percent biochar in a

cassava forage diet with the optimum level at about 0.8 % biochar in DM

3.3. GROWTH AND FEED CONVERSION

Biochar is not a nutrition source for the animals, but it will be an additive effect

on reduction of methane emissions from adding both biochar (increasing the potential

microbial habit) and nitrate to the diet of cattle fed a base diet of fresh cassava root

chips supplemented with fresh cassava leaves (Leng et al., 2012). According to Madsen

et al. (2010) respirede gas from each animal fed biochar was analyzed for methane and

carbon dioxide and live weight gain was increased 25% and feed conversion was

108

improved by biochar also on young local Yellow cattle. In the present results, daily live

weight gain was improved 26% by supplementation with biochar (at 0.86% biochar in

DM intake) and feed conversion of goats according to percent biochar in a cassava

forage diet with the optimum level at about 0.86% biochar in DM, and trend decrease

high level of biochar (1.3% in DM). In addition, the difference was depending on the

quality of biochar (Figure 5.7). According to Leng (2017), Biochar is a byproduct from

the carbonization of fibrous residues at high temperatures. It is composed primarily of

carbon and phenolic compounds and residual minerals from the original biomass. The

large surface area (>30 m2/g), high pH and water-holding capacity, makes it an ideal

site for the adsorption of communities of microorganisms and nutrients in biofilms.

Therefore, the biochar created conditions for the effective detoxification of the

cyanogenic glucosides present in the cassava forage. And biochar increases growth rate

of goats fed foliage of Bauhinia acuminate with and without water spinach Ipomoea

acuatica (Silivong and Preston, 2015).

Table 5.3. Live weight and feed conversion in goats fed increasing levels of biochar in

a diet of fresh cassava forage

Biochar, % in diet DM

SEM

p-value

B0

B0.5

B1.0

B1.5

Live weight, kg

Initial

16.5

16.1

16.7

16.4

0.487

0.83

Final

25.5

26.6

28.3

26.3

0.828

0.18

LW gain, g/d

100b

117ab

129a

111ab

5.04

0.03

FCR

5.66

4.88

5.1

5.39

0.19

0.083

Notes: B0; B0.5; B1.0; B1.5: Treatments supplemented biochar levels of 0;0.5; 1.0; 1.5 (% in diet DM) ab Means without common superscript differ at p<0.05 FCR = DM consumed/weight gain SEM: standard error of the mean; p- value: The level of statistical significance is different

109

160

140

d / g

120

100

y = -51.1x2 + 75.7x + 99.7 R² = 0.675

n i a g t h g i e w e v i L

0.2

0.4

0.6

0.8

1.2

1.4

Biochar, % in DM

Figure 5.6. Curvilinear response of live weight gain of goats to percent biochar in a

cassava forage diet with the optimum level at about 0.86 % biochar in DM

It has been shown that the growth of a biochar test plant (maize) was linearly

related to the water retention capacity of the biochar used as soil amendment (Nguyen

Van Lanh et al. 2019). The fact that growth rates increased when the 4.89 WRC biochar

was fed, as compared with the previous period with 3.81 WRC biochar (Figure 5.7) is an

interesting unsubstantiated observation that merits further research relating to the water

Bio3.81

Bio4.89

y = -52.654x2 + 78.703x + 98.433 R² = 0.7965

y a d / g

y = -22.125x2 + 37.142x + 91.955 R² = 0.4774

n i a g t h g i e w e v i L

160 140 120 100 80 60 40 20 0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Biochar, % in DM

retention capacity of biochar and its relative value as an additive in livestock diets.

3.81 and 4.89 fed in succeeding periods (-15 to + 10 days) and 10-90 days)

Figure 5.7. Growth response curves to biochar with water retention capacities of

110

The 26% increase in growth rate from including 0.86% biochar in the diet of

goats in the present experiment concurs with growth responses observed in: (i) goats

fed legume tree and cassava forage (Silivong et al., 2016) or forages from sweet and

bitter cassava varieties (Phuong et al., 2019); and (ii) in cattle fed cassava roots and

cassava forage (Leng et al., 2012; Sengsouly and Preston, 2016; Saroeun et al., 2018).

Common to all these reports is the presence of cassava forage and cassava roots as a

major component of the diet.

Both roots and forage of cassava contain cyanogenic glucosides that give rise to

toxic HCN when exposed to enzymes in the digestive tract of animals and humans. We

hypothesize that the beneficial effects of biochar on growth of goats and cattle fed

cassava products is because the biochar provides habitat for microbial communities that

reduce the toxic effects of the HCN while still retaining its beneficial effects in

modifying the sites of digestion as discussed by Inthapanya et al. (2019).

3.4. METHANE EMISSION

The ratio of methane and carbon dioxide in eructed gases from goats fed

cassava forage supplemented with different level of biochar are shown in table 5.3,

figure 5.8. This is a smaller response than Leng et al. (2012a) reported with a 24%

reduction in CH4 (ppm) when feeding biochar derived from rice hulls at 0.6% of the

diet DM. Similarly, Saleem et al. (2018) reported a 25% reduction in CH4 (mg/d) from

an artifcial rumen system with 0.5% biochar compared to no biochar.

Table 5.4: The ratio methane: carbon dioxide in eructed gases from goats fed

cassava forage supplemented with biochar

Biochar, % in diet DM

Items

SEM

p-value

B0

B0.5

B1.0

B1.5

982

669

686

709

CO2, ppm

32.4

18.2

16.3

15.7

CH4, ppm

CH4/CO2

0.033a

0.028b

0.025c

0.02d 0.0006

<0.001

Notes: B0; B0.5; B1.0; B1.5: Treatments supplemented biochar levels of 0;0.5; 1.0; 1.5 (% in diet DM) abcd Means without common superscript differ at p<0.05 SEM: standard error of the mean p- value: The level of statistical significance is different

111

0.04

0.035

0.03

y = -0.0041x + 0.0362 R² = 0.992

0.025

0.02

0.015

0.01

o i t a r e d i x o i d n o b r a c : e n a h t e

0.005

0.000

0.360

0.855

1.290

Biochar, % in DM

Figure 5.8. Linear reduction in methane: carbon dioxide ratio in eructed gas of

goats fed up to 1.3% biochar in a diet of cassava forage

The ratio of methane and carbon dioxide was the effect on the rumen

fermentation the improvement (decrease in methane production) was decreased linear

in goats fed increasing levels of biochar in a diet of fresh cassava forage. The results of

the present study agree with other studies that used rice hull-based biochar (Leng et al.,

2012a, b). These studies showed a positive effect of biochar in reducing methane from

rumen microbial feed degradation either in vitro or in vivo. Addition of 1% biochar to a

cassava root meal and urea substrate reduced methane production by 11-13%. In this

study, no further benefits were found with increasing level of biochar between 2% and

5% (Leng et al., 2012a, 2012b). Another study, from the same authors, investigated the

effects of potassium nitrate versus urea as the protein source in a cassava-based diet

with and without 0.6% (DM) rice hull biochar on feed intake, liveweight gains, and

methane production of local, ‘‘Yellow’’ cattle (Leng et al., 2012b). Addition of biochar

products numerically, but not significantly, reduced CH4 production between 11% and

17% compared to without biochar (Hansen et al., 2012). Another study, Digestible

energy intake was not affected by biochar inclusion in the growing or finishing study.

Methane production (g/d) tended to decrease quadratically (P = 0.14) in the growing

study and was decreased 10.7% for the 0.8% biochar (of diet DM and Biochar was

made from whole pine trees) treatment relative to the control (without biochar) in

finishing steer. The control diet consisted of 53% dry-rolled corn, 15% corn silage,

112

25% wet distillers’ grains plus solubles, and 7% supplement (Thomas M. Winders

et al., 2019)

Activated biochar products were hypothesized to be able to stimulate or create a

mechanism to allow for cell wall degradation with a minimum methane output. Because

absorb Lehmann and Joseph (2009) showed that biochar can absorb gases in soils it may

also be able to absorb gases produced in the rumen of ruminants. Biochar is a carbonized

plant material produced by pyrolysis of cellulose-rich biomass and is known to improve

soil properties, absorb gases, and store carbon. Microbial methane production reflects an

energy loss to the animal as well as a GHG emission. As such, there is an increasing

interest in reducing methane production from the rumen of ruminants, and biochar, used

as a feed additive, could be a tool for mitigation. Biochar products may stimulate or

create a mechanism to allow cell wall degradation with minimum methane production.

Results from this study illuminate the need for further studies on the ability of biochar

products qualities to reduce methane production during rumen degradation with many

kinds of biochar products. May be biochar can also reduce greenhouse gas emissions and

ameliorate the contribution of ruminants to global warming.

4. CONCLUSIONS

- Feed intake, live weight gain and feed conversion were improved by

increasing biochar supplementation from 0 to 0.86% of the diet DM followed by a

decline as the biochar level was raised to 1.3% in diet DM.

- Daily live weight gain was icreased 26% by supplementation with biochar at

0.86 % in diet dry matter.

- The ratio of rumen methane emissions and carbon dioxide were reduced

numerically 24% for the 0.86% biochar treatment relative to no biochar.

It is hypothesized that the beneficial effects of biochar on growth of goats and

cattle fed cassava products is because the biochar provides habitat for microbial

communities that reduce the toxic effects of the HCN while still retaining its beneficial

effects in modifying the sites of digestion with positive effects on growth and feed

conversion and in reduction of enteric methane.

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REFERENCES An Giang Statistic office, 2018. Statistic yearbook of An Giang 2017. Youth Publishing

AOAC., 1990. Official Methods of Analysis. 15th ed. AOAC, Washington, DC

AOAC., 2016. Official Methods of Analysis. 20th Edition, Washington D.C.

Binh P. L. T, Preston T. R, Duong K. N. and Leng R. A., 2017. A low concentration (4% in diet dry matter) of brewers’ grains improves the growth rate and reduces thiocyanate excretion of cattle fed cassava pulp-urea and “bitter” cassava forage. Livestock Research for Rural Development. Volume 29, Article #104.

Binh P. L. T., Preston T.R, Van H. N and Dung D.V., 2018. Methane production in an in vitro rumen incubation of cassava pulp-urea with additives of brewers’ grain, rice wine yeast culture, yeast-fermented cassava pulp and leaves of sweet or bitter cassava variety. Livestock Research for Rural Development. Volume 30, Article #77.

Do Thi Thanh Van and Nguyen Van Thu, 2018. Recent Status, Research and Development of Dairy Goat Production in Vietnam. Paper presented at the 4th Asian - Australasian dairy goat Conference. Oct 17-19, 2018. Tra Vinh University, Vietnam

Hansen H. H., Storm I. M. L. D., and Sell A. M. 2012. Effect of biochar on in vitro rumen methane production. Acta Agriculturae Scandinavica, Section A - Animal Science, 62(4), 305–309.

Inthapanya S, Preston T. R, Leng R A, Phung L D and Ngoan L D, 2019. Simulating rice distillers’ by-product with fermented sticky rice; effects on methane production in an in vitro rumen fermentation of ensiled cassava root, cassava forage and urea. Livestock Research for Rural Development. Submitted

Leng R. A., Preston T. R. and Inthapanya S., 2012a. Biochar reduces enteric methane and improves growth and feed conversion in local “Yellow” cattle fed cassava root chips and fresh cassava forage. Livestock Research for Rural Development. Volume 24, Article #199.

Leng R. A., Inthapanya S. and Preston T. R, 2012b. Biochar lowers net methane production from rumen fluid in vitro. Livestock Research for Rural Development. Volume 24, Article #103.

Lehmann J. and Joseph S., 2009. Biochar for environmental management: an introduction. In: J Lehmann, and S Joseph, editors, Biochar for environmental management, science and technology. Earthscan, London. p. 1–12

Madsen J, Bjerg B. S., Hvelplund T. M., Weisbjerg R. and Lund P.., 2010. Methane and carbon dioxide ratio in excreted air for quantification of the methane production from ruminants, Livestock Science 129, 223–227

Minitab, 2016. Minitab user's guide. Data analysis and quality tools. Release 13.1 for windows. Minitab Inc., Pennsylvania, USA.

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Lanh N. V., Bich N. H., Hung B.N., Quyen N. N. and Preston T. R., 2019: Water retention capacity of biochar and its effect on growth of maize. Livestock Research for Rural Development. Volume 31, Article #95.

Olivier P., 2010. The Small-Scale Production of Food, Fuel, Feed and Fertilizer; a Strategy for the Sustainable Management of Biodegradable Waste.

Binh P. L. T., Preston T. R, Van N. H. and Dung D. V., 2019. Effect of additives (brewer’s grains and biochar) and cassava variety (sweet versus bitter) on nitrogen retention, thiocyanate excretion and methane production by Bach Thao goats. Livestock Research for Rural Development. Volume 31, Article #1.

Preston T. R., 2001. Potential of cassava in integrated faming systems. In: Proceedings of International Workshop on Current Research and Development on Use of Cassava as Animal feed. (Editors: T R Preston, B Ogle and M Wanapat), organized by Khon Kaen University and SIDA- SAREC, Sweden. July23-24, 2000

Saroeun K, Preston T R and Leng R A., 2018. Rice distillers’ byproduct and molasses- urea blocks containing biochar improved the growth performance of local Yellow cattle fed ensiled cassava roots, cassava forage and rice straw. Livestock Research for Rural Development. Volume 30, Article #162.

Saleem, A. M., Ribeiro Jr. G. O., Yang W. Z., Ran T., Beauchemin K. A., McGeough E. J., Ominski K.H., Okine E.K. and McAllister T. A., 2018. Effect of engineered biocarbon on rumen fermentation, microbial protein synthesis, and methane production in an artificial rumen (RUSITEC) fed a high forage diet1. Journal of Animal Science. 96:3121–3130.

Sengsouly P. and Preston T R., 2016. Effect of rice-wine distillers’ byproduct and biochar on growth performance and methane emissions in local “Yellow” cattle fed ensiled cassava root, urea, cassava forage and rice straw. Livestock Research for Rural Development. Volume 28, Article #178.

Silivong P. and Preston T R., 2015. Growth performance of goats was improved when a basal diet of foliage of Bauhinia acuminata was supplemented with water spinach and biochar. Livestock Research for Rural Development. Volume 27, Article #58.

Silivong P. and Preston T R., 2016. Supplements of water spinach (Ipomoea aquatica) and biochar improved feed intake, digestibility, N retention and growth performance of goats fed forage of Bauhinia acuminata as the basal diet. Livestock Research for Rural Development. Volume 28, Article #98.

Silivong P., Preston T. R, Van N. H and Hai D. T., 2018. Brewers’ grains (5% of diet DM) increases the digestibility, nitrogen retention and growth performance of goats fed a basal diet of Bauhinia accuminata and forage from cassava (Manihot esculenta Crantz) or water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 30, Article #55.

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Sina V., Preston T. R. and Tham T. H.., 2017. Brewers’ grains have a synergistic effect on growth rate of goats fed fresh cassava forage (Manihot esculenta Crantz) as basal diet. Livestock Research for Rural Development. Volume 29, Article #137.

Thuy Hang L. T., Preston T. R., Leng R. A and Ba N. X., 2018. Effect of biochar and water spinach on feed intake, digestibility and N-retention in goats fed urea- treated cassava stems. Livestock Research for Rural Development. Volume 30, Article #93.

Thomas M. Winders, Melissa L. Jolly-Breithaupt, Hannah C. Wilson, James C. MacDonald, Galen E. Erickson, and Andrea K. Watson, 2019. Evaluation of the effects of biochar on diet digestibility and methane production from growing and finishing steers. American Society of Animal Science. 2019.3:775–783.

Van Soest P. J., Robertson J. B. and Lewis B. A., 1991. Methods for Dietary Fiber, Neutral Detergent Fiber, and Nonstarch Polysaccharides in Relation to Animal Nutrition. In: Symposium: Carbohydrate methodology, metabolism, and nutritional implications in dairy cattle. Journal of Dairy Science, Volume 74: 3583 – 3597.

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CHAPTER 6 GENERAL DISCUSSION AND CONCLUSIONS

1. GENERAL DISCUSSION

1.1. POTENTIAL OF CASSAVA IN VIETNAM

Cassava (Manihot esculenta Crantz) is a major crop in Vietnam, grown on

532,501 ha producing annually some 1 million tonnes of roots (FAOSTAT, 2017). The

roots are used mainly for manufacture of starch and as an ingredient in livestock feed. At

the time of root harvest, the cassava forage (leaves and petioles) and cassava stems

remain as a byproduct. The stems are used partly as plant material for the next crop, but

the greater part is discarded after root harvest. The ready availability of this waste

product has led to experiments in our laboratory to utilize them as the basal diet for goats.

Figure 6.1. Forage and stems that remain

when the cassava roots are harvested

Growing the crop as a semi-perennial forage with repeated harvesting at 2 to

3month intervals is a recent development (Wanapat, 1997; Preston et. al., 2000; San Thy

and Preston, 2001). Feeding goats with fresh cassava forage was pioneered in Cambodia

where it was shown to be a means of controlling strongyle infection as well as supporting

good growth rates (Kerya et al., 19--). More recently it was fed as the primary diet of

growing goats with growth rates reaching 160 g/day when it was supplemented with

small quantities of brewers’ grains (4% of diet DM) (Vor Sina et al., 2017). Further

developments (Phuong et al., 2018) with goats highlighted the potential benefits from

supplementing the cassava forage with biochar, the byproduct of the carbonization of

biomass at high temperatures (Lehmann, 2005) and this was particularly effective when

the cassava forage was from a “bitter” variety with a high concentration of cyanogenic

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glucosides. Phalla (2007) had earlier shown that cassava stems were as effective as other

sources of fibrous biomass for the production of biochar.

The aims of this thesis were to provide more information on the use of the

different parts of the cassava plant as the basal diet of growing goats.

1.2 EFFECT ON NUTRITIVE VALUE OF CASSAVA (MANIHOT ESCULENTA

CRANTZ) STEMS OF ENSILING THEM WITH UREA

Cassava stems contain about 33% DM but only about 6% crude protein (CP) in

the DM. It was therefore hypothesized that there could be a double benefit from

ensiling the cassava stems with urea: (i) to provide the ammonia needed by rumen

organisms; and (ii) to improve the digestibility of the stems DM as has been widely

proven in the urea-ensiling of low-protein, fibrous feeds such as rice straw.

The positive effects of storing (ensiling) the cassava stems with addition of urea

were the reduction in HCN levels and the possible synthesis of protein from the

ammonia derived from the urea. On the negative side was the considerable loss of

biomass (about 24%) resulting from the fermentation of part of the cassava stems

carbohydrate.

1.3 DIGESTIBILITY, NITROGEN BALANCE AND METHANE EMISSIONS

IN GOATS FED CASSAVA FORAGE AND RESTRICTED LEVELS OF

BREWERS’ GRAINS

This experiment was designed to provide evidence for the prebiotic effect of

brewers’ grains in a basal diet of cassava forage fed to growing goats. Proportions of

ensiled brewers’ grains above (6%) and below (2%) the 4% level were compared to

identify the optimum level.

Four “Bach Thao” goats (14 ± 2 kg) were fed fresh cassava forage (sweet

variety) ad libitum and 4 levels (0, 2, 4 and 6%, DM basis) of brewers’ grains in a 4*4

Latin square changeover design with periods of 14 days.

Adding 4% of brewers’ grains to the diet of cassava forage increased the DM

intake, the apparent DM digestibility, the N retention and the biological value of the

absorbed nitrogenous compounds. The methane levels in eructed gas decreased with a

curvilinear trend as the proportion of brewers’ grains in the diet was increased. The

benefits of small quantities of brewers’ grains in the diet are believed to be related to

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their “prebiotic” qualities in enhancing the action of beneficial microbial communities

along the digestive tract of the animal.

1.4 EFFECT OF BIOCHAR AND WATER SPINACH ON FEED INTAKE,

DIGESTIBILITY AND N-RETENTION IN GOATS FED UREA-TREATED

CASSAVA STEMS

In the first reported study on addition of 1% of biochar in the diet of ruminants

(Leng et. al., 2012), growth rates were increased 20% but were probably constrained by

errors in management of the feed resource (fresh cassava root) that probably propitiated

growth of mycotoxins. More recent studies have shown synergistic effects from

combining biochar with rice distillers’ byproduct in a cassava-based diet for fattening

cattle (Sengsouly et al., 2016) and by combining biochar with water spinach in diets of

goats (Silivong et al., 2015, 2016).

On the basis of this background, the present experiment was designed with the

aim of determining if the synergistic effects of biochar and water spinach on growth of

goats fed forage of Bauhinia accuminata would be equally manifested when the basal

diet was composed of urea-treated cassava stems, shown to be a potential feed resource

for goats by Thanh et al., (2013).

Four “Bach Thao” goats (LW 14 ± 2 kg) were fed urea-treated cassava stems

alone (UCS) or with a supplement of water spinach at 1% of LW (DM basis) (UCSW),

with biochar (derived by carbonization of rice husks in an updraft gasifier stove) at 1%

of DM intake (UCSB) or with water spinach + biochar (CSWB). The design was a

Latin square with four treatments and four periods, each lasting 15 days (ten days for

adaptation and 5 days for collection of feces and urine).

Urea treatment of the cassava stems increased the crude protein from 5.5 to

11.7% in DM. DM intake was increased 18% by supplementing the urea-treated

cassava stems with biochar. Addition of water spinach increased total DM intake by

25% while the combined effect of biochar plus water spinach was to increase intake by

41%. Biochar increased daily N retention by 46% and the biological value of the

absorbed N by 12%.

Biochar provides no protein to the diet, thus it was postulated that the increase

in N retained and in its biological value came about as a result of the biochar

stimulating rumen microbial growth resulting in an increase in synthesis and hence of

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absorption of amino acids. We suggest this is further evidence that biochar effectively

functions as a “prebiotic” – stimulating the activity of beneficial microbial communities

through its support for biofilms in the digestive tract of the animal.

1.5. EFFECT OF BIOCHAR ON GROWTH AND METHANE EMISSIONS OF

GOATS FED FRESH CASSAVA FORAGE.

The hypothesis underlying the research was that there would be a dose response

in growth rate to biochar over the range of 0 to 1.5% in diet DM.

Twelve growing male goats of the Bach Thao breed, with an initial body weight from

14 to 16 kg, were housed in individual cages and given a basal diet of ad libitum fresh

cassava forage (sweet variety) supplemented with 4% (DM basis) of ensiled brewers’

grain. The length of the trial was 12 weeks after a period of 10 days to accustom the

goats to the diets.

For all the growth criteria (feed intake, live weight gain and feed conversion),

the responses were curvilinear with positive effects from increasing biochar

supplementation from 0 to 0.8% of the diet DM followed by a decline as the biochar

level was raised to 1.3% in diet DM. By contrast, in terms of effects on the rumen

fermentation the improvement (decrease in methane production) was linear.

It is concluded that the beneficial effects of biochar on growth of goats and

cattle fed cassava products is because the biochar provides habitat for microbial

communities that reduce the toxic effects of the HCN (or its precursors) while still

retaining its beneficial effects in modifying the sites of digestion with positive effects

on growth and feed conversion.

2. GENERAL CONCLUSIONS

- The positive effects of storing (ensiling) the cassava stems with addition of

urea are the reduction in HCN levels and the possible synthesis of protein from the

ammonia derived from the urea and the fermentation of part of the carbohydrate in the

cassava stems. Urea treatment of the cassava stems (with 3% in DM) increased the

crude protein from 5.5 to 11.7% in DM and can be preserved up to 8 weeks.

- Cassava stems treated with 3% urea in DM improves nutrietive value and DM

intake up to 18% by supplementing with biochar. Addition of water spinach increased

total DM intake by 25% while the combined effect of biochar plus water spinach was to

increase intake by 41%. Biochar increased daily N retention by 46% and the biological

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value of the absorbed N by 12%. Biochar provides no protein to the diet, thus it is

postulated that the increase in N retained and in its biological value came about as a

result of the biochar stimulating rumen microbialgrowth resulting in an increase in

synthesis and hence of absorption of amino acids.

- Adding 4% of brewers’ grains to a diet of cassava forage increased the DM

intake, the apparent DM digestibility, the N retention and the biological value of the

absorbed nitrogenous compounds. The benefits of such small quantities of brewers’

grains are believed to be related to their “prebiotic” qualities in enhancing the action of

beneficial microbial communities along the digestive tract of the animal.

- Feed intake, live weight gain and feed conversion were improved by

increasing biochar supplementation from 0 to 0.8% of the diet DM followed by a

decline as the biochar level was raised to 1.3% in diet DM. Rumen methane emissions

were reduced with a linear trend as the level of biochar in the diet was increased.

3. IMPLICATION AND FUTHER RESEARCH

3.1 IMPLICATIONS

The research described in this thesis adds to the increasing degree of

appreciation that the cassava crop can play the same role in the tropics that is played by

maize in temperate latitudes, as the basis for more intensive systems of ruminant

production. It has been shown in the research reported in thesis, cassava offers more

products useful to animal production than does maize: (i) the root is a proven

replacement carbohydrate for maize grain; (ii) the forage from cassava is an excellent

source of bypass protein for intensification of ruminant productivity; (iii) the stems can

be the basal diet of growing goats as well as being a potential source of renewable

energy by gasification to a combustible gas (Phalla, 2007). By contrast, the forage

from maize is of negligible value at the time of harvesting the grain. An additional

factor in favor of cassava is that it is more tolerant to high ambient temperatures and is

not likely to suffer the decline in yield, as is the case predicted for maize, as a result of

climate change (Jarvis et al., 2012).

A major issue that has developed from the research with cassava forage is the

role of the cyanogenic glucosides present in both roots and forage of cassava that can

give rise to toxic HCN when exposed to enzymes in the digestive tract of animals and

humans. On the other hand, the presence of these cyanogenic glucosides has been

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shown to be associated with benefits such as reduction in total gas and methane by

rumen organisms (Binh et al., 2017). In Paper 3, we hypothesized that the beneficial

effect of biochar on growth of goats was because the biochar provides habitat for

microbial communities that reduce the toxic effects of the HCN while still retaining its

beneficial effects in modifying the sites of digestion as discussed by Inthapanya et al.,

(2019). The concept is that low levels of cyanogenic glucosides act to reduce the rate of

rumen fermentation thus facilitating rumen escape of protein for more efficient

enzymic digestion in the small intestine, while potentially fermentable carbohydrate

continues to the cecum where the fermentation is acetogenic such that losses as

methane are avoided. A recent paper from Houda et al., (2017) describes a similar shift

in digestion sites as a result of including small amounts of thymol in the diet pf

lactating cows. In vitro rumen gas production was reduced by the additive, milk

production was increased and methane in eructed gas was reduced.

3.2 FUTURE RESEARCH

The new information that has resulted from this research is the role of additives

such as brewers’ grains and biochar which appear to act in the ruminant animal as

“prebiotics”, that “facilitate” the activity of the resident microflora or act by

sequestering toxic substances such as mycotoxins and other anti-nutritional compounds

such as the precursors of hydrocyanic acid (HCN).

The research in this thesis has been with “sweet” varieties of cassava which

have lower concentrations of HCN precursors than the “bitter” varieties (Phuong et al.,

2019). However, bitter varieties have higher yields of roots than the sweet varieties

and are exclusively planted when the aim is industrial starch production (reference).

Relevant observations are that goats having free access to forage of both sweet and

bitter varieties opted to consume equal proportions of each (Phuong et al., 2019),

despite observations elsewhere (Chiv Phiny., 2019), that when goats were fed

exclusively on bitter cassava forage there was high mortality caused by HCN toxicity.

The fact that growth rates, as measured by N retention, were better and that methane in

eructed gases was reduced, for the 50:50 balance of sweet and bitter varieties compared

with a sweet variety fed alone, is further justification for promoting research equally

with bitter and sweet varieties. In such research, the relative responses to prebiotic

additives should have high priority.

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The final issue that requires research – and which should have highest priority –

concerns the role of biochar in sequestering atmospheric carbon dioxide. Biochar

contains of the order of 60% carbon derived from the atmosphere and which, applied

directly to soils, is resistant to further oxidation – hence its role in mitigation of climate

change by sequestering atmospheric carbon dioxide. It is assumed that, because of its

resistance to further chemical change, biochar fed to animals will be excreted largely

unchanged and that when retuned to soil as fertilizer, the excreta from animals fed

biochar will continue to have beneficial effects on soil fertility as well as a continued

role in sequestering carbon. The area of research should have high priority.

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REFERENCES

Binh P. L.T., Preston T. R, Khang D.N. and Leng R. A., 2017. A low concentration (4% in diet dry matter) of brewers’ grains improves the growth rate and reduces thiocyanate excretion of cattle fed cassava pulp-urea and “bitter” cassava forage. Livestock Research for Rural Development. Volume 29, Article #104.

Binh P. L. T., Preston T. R, Van N.H and Dung D.V., 2018. Methane production in an in vitro rumen incubation of cassava pulp-urea with additives of brewers’ grain, rice wine yeast culture, yeast-fermented cassava pulp and leaves of sweet or bitter cassava variety. Livestock Research for Rural Development. Volume 30, Article #77.

FAOSTAT, 2017. FAO Statistical Database. (Food and Agriculture Oranization of the United Rome).

Inthapanya S, Preston T R, Leng R A, Phung L D and Ngoan L D, 2019. Simulating rice distillers’ by-product with fermented sticky rice; effects on methane production in an in vitro rumen fermentation of ensiled cassava root, cassava forage and urea. Livestock Research for Rural Development. Submitted

Leng R. A, Preston T. R. and Inthapanya S., 2012. Biochar reduces enteric methane and improves growth and feed conversion in local “Yellow” cattle fed cassava root chips and fresh cassava forage. Livestock Research for Rural Development. Volume 24, Article #199.

Binh P.L T., Preston T. R, Van N. H. and Dung D. V., 2019. Effect of additives (brewer’s grains and biochar) and cassava variety (sweet versus bitter) on nitrogen retention, thiocyanate excretion and methane production by Bach Thao goats. Livestock Research for Rural Development. Volume 31, Article #1.

Silivong P., Preston T. R., Van N. H. and Hai D. T., 2018. Brewers’ grains 5% of diet DM) increases the digestibility, nitrogen retention and growth performance of goats fed a basal diet of Bauhinia accuminata and forage from cassava (Manihot esculentaCrantz) or water spinach (Ipomoea aquatica). Livestock Research for Rural Development. Volume 30, Article #55.

124

Sina V., Preston T R. and Tham T. H., 2017. Brewers’ grains have a synergistic effect on growth rate of goats fed fresh cassava forage (Manihot esculenta Crantz) as basal diet. Livestock Research for Rural Development. Volume 29, Article #137.

Thanh T. X., Hue K. T, Anh N N. and Preston T. R., 2013. Comparison of different forages as supplements to a basal diet of chopped cassava stems for growing goats. Livestock Research for Rural Development. Volume 25, Article #7.

Wanapat M., Pimpa O., Petlum A. and Boontao U., 1997. Cassava hay: A new strategic feed for ruminants during the dry season. Livestock Research for Rural Development 9(2), 1-5.

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PUBLICATION LIST

This thesis is based on the work contained in the following papers:

Paper 1: Digestibility, nitrogen balance and methane emissions in goats fed cassava

forage and restricted levels of brewers’ grains. Livestock Research for Rural

Development. Volume 30, Article #68 from

http://www.lrrd.org/lrrd30/4/thuy30068.html

Paper 2: Effect of biochar and water spinach on feed intake, digestibility and N-

retention in goats fed urea-treated cassava stems. Livestock Research for Rural

Development. Volume 30, Article #93. from

http://www.lrrd.org/lrrd30/5/thuyh30093.html

Paper 3: Effect of biochar on growth and methane emissions of goats fed fresh cassava

forage. Livestock Research for Rural Development. Volume 31, Article

#67. from

http://www.lrrd.org/lrrd31/5/thuyhang31067.html

Paper 4: Effect on nutritive value of cassava (Manihot esculenta Crantz) stems of

ensiling them with urea. Livestock Research for Rural Development. Volume 31,

Article #92. from

http://www.lrrd.org/lrrd31/6/thuyh31092.html

126

APPENDICES

Experiment 2: Cassava stems untreated and treated with difference level of urea (0, 1,2,3 and 4% in DM)

Cassava stems before and after mixing urea

0% urea 1% urea 3% urea 4% urea 2% urea After two weeks storing

0% urea 1% urea 2% urea 3% urea 4% urea

After 4 weeks storing

0% urea 1% urea 2% urea 3% urea 4% urea After 6 weeks storing

0% urea 1% urea 2% urea 3% urea 4% urea

After 8 weeks storing

Experiment 4 & 5: