Luận án 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
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 of Livestock Research for Rural Development (LRRD)  
	 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. 
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 
TABLE OF CONTENTS
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
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
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 1	64
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
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 
ADF
Acid detergent fiber
ATP
Adenosine triphosphate
BW
 Body weight
BSP
 Brewery spent grain
CP
 Crude protein
CT
 Condensed tannins 
CNP
 Cyanogenic potential
CH4
 Methane
CO2
 Carbon dioxide 
DM
 Dry matter
EPG
 Eggs per gram
FW
Fresh weight
GHG
Green house gas 
EPS
 Self-produced polymeric substance
HT
 Hydrolysable tannins
HCN
 Hydrogen cyanide
LW
 Live weight
N
 Nitrogen
ND
No detection 
NDF
Neutral ditergent fiber
SCFA
 Short -chain fatty acid
TMR
Total mix ration
VFA
 Volatile fatty acid
WRC
Water retention capacity
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  ... ), 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 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 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 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. 
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.
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. 
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., 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. 
Silivong P. and Preston T. R., 2015. Growth performance of goats was improved when a basal diet of forage 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. 
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.
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
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 
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 
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 
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
2% urea
3% urea
4% 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: 
A wood frame covered with clear glass and Gasmet infra-red meter (GASMET 4030