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Effect on nutritive value of cassava (Manihot esculenta
Crantz) stems of ensiling them with urea
Le Thi Thuy Hang and T R Preston1
Department of Animal Sciences and Veterinary Medicine, Agricultural and Natural
Resources Faculty, An Giang University, Vietnam

1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria
(CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract
Cassava 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. The stems contain
about 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 stem
DM as has been widely proven in the urea-ensiling of low-protein, fibrous feeds such as rice
straw. The treatments in a random block 5*5 factorial design were: (a) five levels of urea (0,
1, 2, 3 and 4%, DM basis) added to freshly chopped cassava stems; and (b) five storage
times (0, 2, 4, 6 and 8 weeks). Each treatment combination was replicated 4 times.
The positive effects of storing (ensiling) the cassava stem with addition of urea were 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. On the
negative side was the considerable loss of biomass (about 24%) resulting from the
fermentation of part of the cassava stem carbohydrate stimulated by the availability of
ammonia from the added urea.
Key words: ammonia, fermentation, HCN, protein, tannins

Introduction
Cassava (Manihot esculenta Crantz) is a perennial woody shrub of the family
Euphorbiaceae. It originated in the Caribbean 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 foliage as a feed for animals. Cassava foliage is
recognized as a source of bypass protein with a high content of digestible nutrients for both
non-ruminants and ruminants (Wanapat 1997). 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). At root harvest, 9 to 10 months after planting, the foliage production can be about 5
tonnes dry matter (DM)/ha (Mui 1994) . It is estimated that more than 2.5 milion tonnes of
cassava foliage are produced in Vietnam, of which about 15,000 tonnes in An Giang,
Cassava foliage 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
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toxicity symptoms in animals when the tolerated dose is exceeded.
Cassava foliage consists of the leaves, petioles and small branches which attach to the highly
lignified stem. Observations at the Rabbit and Goat Center in Bavi, North Vietnam indicated
that the stem was 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 foliage
supported live weight gains in growing goats of 57 g/day, 100% higher than when Guinea

grass was used to supplement the cassava stems.
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 stem DM as has been widely proven in
the urea-ensiling of low-protein, fibrous feeds such as rice straw (Trach et al 1998).
The specific objectives were to determine if the addition of urea to cassava stems would
facilitate the storage of this feed resource and at the same time improve its digestibility.

Material and methods
The experiment was carried out at An Giang University in An Giang Province in the South
of Vietnam from March to June 2015.
Treatments and experimental design
The treatments in a random block 5*5 factorial design were: (a) five levels of urea (0, 1, 2, 3
and 4%, DM basis) added to freshly chopped cassava stems; and (b) five storage times (0, 2,
4, 6 and 8 weeks). Each treatment combination was replicated 4 times. Cassava stems were
collected from farmers’ fields directly after root harvesting and chopped by hand.
Representative amounts were analyzed for DM by infra-red 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.
After the appropriate storage times, samples of the treated stems were taken for measurement
of pH (ORION model 420 A) and proximate composition. The DM, ash and HCN content
were determined according to the standard methods of AOAC (2016). Nitrogen was
determined by the Kjeldahl procedure. NDF and ADF were analysed according to the
procedure of Van Soest et al(1991). Total tannin content was determined according to the
method (955.35) of AOAC (2016).
Statistical analysis
The data were subjected to an analysis of variance (ANOVA) using the General Linear
Model (GLM) procedure of Minitab 16. Sources of variation were levels of urea, storage
time, the interaction urea levels*storage time and random error.

Results and discussion
There were major effects of urea level and storage time on chemical attributes of the urea-

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ensiled cassava stems (Tables 1, 2 and 3; Figures 1 – 8).
Table 1. Mean values for effects of urea level on composition of the ensiled cassava stems
Urea
Tannin
HCN
NDF
ADF
CP
Ammonia
pH
%
%
mg/kg
%
%
%
0
1.24
80.2
0.04
5.31
63.8
50.6

5.82
1
1.09
65.8
0.64
6.70
61.7
49.8
8.12
2
1.10
61.4
0.80
7.09
60.8
49.2
8.99
3
1.02
63.1
0.90
7.82
59.8
48.7
12.5
4
1.05
59.8
1.09
7.91

59.8
47.5
13.7
SEM
0.025
0.699
0.006
0.099
0.147
0.157
0.0615
p
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001
<0.001

Table 2. Mean values for effects of storage time on composition of the ensiled cassava stems
Storage,
Tannin
HCN
NDF
ADF
CP
Ammonia
pH
weeks

%
mg/kg
%
%
%
0
1.24
144
0.09
6.38
65.6
50.5
8.05
2
1.18
130
1.65
7.41
61.0
50.0
10.3
4
1.02
47
0.59
7.52
60.0
48.6
10.6
6

1.04
9.33
0.57
7.12
59.7
48.6
10.2
8
1.01
0.00
0.57
6.40
59.6
48.2
10.0
SEM
0.025
0.699
0.0058
0.099
0.147
0.157
0.0615
p
<0.001
<0.001
<0.001
<0.001 <0.001 <0.001 <0.001

The content of tannin was reduced after 4 weeks of storage and the effect tended to be

greater the higher the level of urea (Figure 1).

Figure 1. Effect of urea level and storage time on tannins in cassava stems

The content of HCN in the stems was reduced gradually over the first two weeks and then
more rapidly after 4 weeks with none being detected after 6 weeks of storage (Figure 2).

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Figure 2. Effect of urea level and storage time on HCN in cassava stems

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 (Figure 3).

Figure 3. Effect of urea level and storage time on ammonia in cassava stems

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 (Figure 4).
Within storage times the pH was positively related to the level of urea added at the beginning
of storage.

Figure 4. Effect of urea level and storage time on pH in cassava stems

After the second week of storage, NDF and ADF levels were reduced linearly by increasing
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levels of urea and by length of storage time; however, the changes were of relatively small
order (Figures 5 and 6).

Figure 5. Effect of urea level and storage time on NDF in cassava stems

Figure 6. Effect of urea level and storage time on ADF in cassava stems

As expected, the crude protein level in the stems was related linearly to the proportion of
urea added at the beginning (Figure 7). There were only slight reductions in overall CP
levels with length of storage

Figure 7. Effect of urea level and storage time on crude protein in cassava stems

Urea level had no effect on the DM content of the cassava stems during the first two weeks
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of storage, when the DM content of the cassava stems did not change (Table 3); 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 (Figure 8).
Table 3. Mean values for effect of storage time and level of added urea
on the DM percentage in the cassava stems
Storage time, weeks
SEM
p
0
2
4
6
8
DM, %
23.6

23.5
22.4
18.4
18.7
0.235 <0.0001

DM, %

0.0
22.1

% urea in DM
1.0
2.0
3.0
21.0
21.7
21.3

4.0
20.6

0.235

<0.0001

Figure 8. Effect of urea level (0 to 4% in DM) and storage
time on the DM content in the cassava stems

Discussion

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).
The decrease in tannin with urea treatment is likely to be a result of the high pH caused by
evolution 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).
The decrease in HCN with storage time may similarly be the 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).
The data for crude protein (N*6.25) is misleading as they do not differentiate between true
protein and the products of multiplying the N 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%; Figure
8). The slight decline in the percentages of NDF (about 10%) and ADF (4%) account for
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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.

Conclusions
The positive effects of storing (ensiling) the cassava stem 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.

On the negative side is the considerable loss of biomass (about 24%) resulting from
the fermentation of part of the cassava stems stimulated by the availability of ammonia
rom the added urea.

References
Alan J D and John A M 1993 Effect of oral administration of brassica secondary metabolites allyl cyanide,
allyl isothocyanate and dimethyl disulphide, on the voluntary food intake and metabolism of sheep. British
Journal of Nutrition 70, 631-645
AOAC 2016 Association of offic ial Analytical chemists. (20th Ed.), Washington, DC
Huertas M J, Sáez L P, Roldán M D, Luque-Almagro V M, Martínez-Luque M, Blasco R, Castillo F,
Moreno-Vivián C and García-García I 2010 Alkaline cyanide degradation by Pseudomonas
pseudoalcaligenes CECT5344 in a batch reactor. Influence of pH. J Hazard Mater. 2010 Jul 15;179(1-3):72-8.
doi:10.1016/j.jhazmat.2010.02.059. Epub 2010 Feb 25.
Makkar H P S 2003a Quantification of Tannins in Tree and Shrubs Foliages—A Laboratory Manual. Kluwer
Academic Press Dordrecht, The Netehrland, p. 102.
Makkar H P S 2003b Effects and fate of tannins in ruminant animals, adaptation to tannins, and strategies to
overcome detrimental effects of feeding tannin-rich feeds. Small Ruminant Res. 49, 241–256.
Mui N T 1994 Economic evaluation of growing Elephant grass, Guinea grass, Sugarcane and Cassava as
animal feed or as cash crops on Bavi high land. In: Proceeding on Sustainable Livestock Production on Local
Feed Resources. Agricultural Publishing House, 16-19
Phengvichith V and Ledin I 2007 Effect of a diet high in energy and protein on growth, carcase
characteristics and parasite resistance in goats. Tropical Animal. Health Production 39, 59–70
Poulton J E 1988 Localization and catabolism of cyanogenic glycosides. In: Cyanide Compounds in Biology,
pp. 67-91. DOI:10.1002/9780470513712.ch6
Price M L, Butler L G, Rogler J C and Featherston W R 1979 Overcoming the nutritionally harmful effects
of tannin in sorghum grain by treatment with inexpensive chemicals. J. Agric. Food Chem. 27, 441–445.
Rawel H M Rohn S and Kroll J 2000 Reactions of selected secondary plant metabolites (glucosinolates and
phenols) with food proteins and enzymes—influence on physico-chemical protein properties, enzyme activity
and proteolytic degradation. Recent Res. Devel. Phytochem. 4, 115–142.
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. />Thuy Hang L T, Man N V and Wiktorsson H 2005 Fresh rice straw treated with urea and lime as feed for
dairy cattle in An Giang province, Vietnam. MSc. Thesis. Department of Animal Nutrition and Management.
Swedish University of Agricultural Science

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Trach N X, Dan C X, Ly L V and Sundstøl F 1998 Effects of urea concentration, moisture content and
duration of treatment on chemical composition of alkali treated rice straw. Livestock Research for Rural
Development. Volume 10, Article #9. />Undersander D, Mertens, D R and Thiex N 1993 Forage Analayses Procedures.National forage Testing
Association, Omaha.
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. Journal of Dairy Science 74(10), 3583-3597.
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.
/lrrd9/2/metha92.htm

Received 20 May 2019; Accepted 20 May 2019; Published 4 June 2019
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Livestock Research for Rural Development 30 (5) 2018

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Effect of biochar and water spinach on feed intake, digestibility and N-retention in goats fed
urea-treated cassava stems
Le Thi Thuy Hang, T R Preston1, R A Leng2 and Nguyen Xuan Ba3
Faculty of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam

1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
2 University of New England, Armidale, NSW 2351, Australia
3 Hue College of Agriculture and Forestry, Hue University, Vietnam

Abstract
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 is 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 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.
Key words: biofilms, biological value, microbial communities, prebiotic

Introduction
Major advances have been made recently in the integrated use of the cassava plant as a means of intensifying ruminant livestock production. A
system of fattening cattle intensively on cassava pulp (the residue after industrial starch extraction) was developed by Phanthavong et al (2014,

2015), in which urea provided rumen fermentable ammonia and bypass protein was supplied by brewers’ grains at 30% of the diet. In a follow-up
series of experiments it was shown that fresh cassava foliage 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 foliage (Inthapanya et al 2016; Binh et al 2017). The system was 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 foliage (Sina et 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 system 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 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 foliage 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).

Materials and methods
Experimental design
The experiment was conducted from June to September 2015 at An Giang University farm, An Giang province, Vietnam. 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 water spinach + biochar (CSWB). The design was a Latin square (Table 1) with four treatments and
four periods, each lasting 17 days (12 days for adaptation and 5 days for collection of feces and urine).
Table 1. The layout of the experiment
Period
Goat 1
Goat 2

1
UCS
UCSW
2
UCSW
UCSWB
3
UCSWB
UCSB
4
UCSB
UCS

Animals and management

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Goat 3
UCSWB
UCSB
UCS
CSW

Goat 4
UCSB
UCS
UCSW
UCSWB

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.
Feeds and feeding
The cassava (sweet variety) was planted 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; Photo1) were harvested at 30-40cm 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 (Photo 2), mixed with urea (3% DM basis; no water was added) and ensiled in closed plastic
bags after first extracting the air (Photo 4). They were ensiled for 21 days (Photo 5), after which they were fed ad libitum as the basal diet of the
goats (Photo 6).

Photo 1. Freshly harvested
cassava stems

Photo 2. Chopping into
5-10 cm lengths

Photo 3. Urea added at
3% of stem DM

Photo 4. Chopped stems-urea are put in
polyethylene bags and the air extracted

Photo 5. Urea-treated stems
are stored for 21 days

Photo 6. Urea-treated stems after
21-day storage ready for feeding

The biochar was made by combusting rice husks in an updraft gasifier stove (Photo 7). The chosen amounts were offered twice daily in troughs
separate from the cassava stem (Photo 8).

Before starting the experiment, it took several days to accustom the goats to eat the biochar. First, biochar was mixed with small quantities of rice
bran and water spinach. After, 3-4 days all the goats were eating this mixture. Then the rice bran and water spinach were gradually removed over
the following 3-4 days. During the experiment, when the diets were changed from “no biochar” to “biochar” [eg: “UCSW to UCSWB] it required
only 1 to 2 days for the goats to adapt to the biochar as they had already been accustomed to eat it before the experiment began.

Photo 7. The biochar was the residue from rice husks used as fuel in a gasifier stove (Paul Olivier)

Photo 8. Biochar, water spinach and urea-treated cassava stems were fed in separate troughs

Feed refusals were weighed every morning prior to giving the new feed. Samples of each diet component were taken daily, stored at -18C, and

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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 am and 16:00pm and added to jars containing 100 ml of
10% (v/v) 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.
Statistical analysis
Data were analyzed with the General Linear Model option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of variation
were treatments, animals, periods and error.

Results and discussion
Composition of the diet ingredients
Urea-treatment of the cassava stems doubled the crude protein content (Table 2). The WRC value (water retention capacity) of 4.4 liters of water
per 1 kg of biochar is 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 2. Chemical composition of diet ingredients (UCS is urea-treated cassava stems

% in DM
DM,
WRC
pH
%
CP
ADF
NDF
OM
CS
33.4
5.50
51.8
66.30
93.5
UCS
23 .0
11.7
51.4
67.1
92
6.92
Water spinach
13.6
18.1
27.6
36.2
93.4
Biochar
4.60

WRC Water retention capacity

DM intake was increased 18% by supplementing the urea-treated cassava stems with biochar which was fed separately {Photo 8) at 1% of the diet
DM (Table 3; Figure 1). 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%.

Figure 1. Effect of biochar on DM intake goats fed urea-treated cassava stems,
with or without fresh water spinach and with or without biochar

Table 3. Mean values of feed DM intake (DMI)in goats fed urea-treated cassava stems,
with or without fresh water spinach and with or without biochar
Treatment
SEM
p
UCS
UCSB
UCSW
UCSWB
UCS
15.0
0.002
367a
428a
300b
352ab
Biochar
0
3.84
0
3.91

Water spinach
0
0
159
163
Total
20.0
0.009
367b
432ab
459ab
518a
0.048
<0.001
DMI, % LW
2.27d
2.59c
2.83b
3.12a

abcd Means within rows without common superscripts differ at p<0.05

Coefficients of apparent DM digestibility were increased more by biochar (by 9%) than by water spinach (2.4%) (Table 4; Figures 2 and 3). The
combined effect of biochar plus 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 4. Mean values of apparent digestibility coefficients (%) 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.
UCS
UCSB

UCSW
UCSWB
SEM
p
Dry matter (%)
0.88
<0.001
59.4b
64.8a
60.8b
66.3a
Crude protein
1.54
<0.010
53.2b
60.1a
59.3a
63.1a
1.78
0.066
Organic matter
59.4b
65.0 a
61.6 ab
66.8 a

ab, Means within rows without common superscripts differ at P<0.05

Table 5. Mean values for N balance in goats fed urea-treated cassava stem supplemented with or
without fresh water spinach (1% of LW, DM basis) and biochar at 1% of DM intake.

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UCS
UCSB
UCSW
UCSWB
N balance, g/d
Intake
8.13d
9.23c
12.4b
13.0a
Feces
3.79b
3.659b
5.099a
4.81a
Urine
1.30
1.17
1.42
1.25
Retention
3.03d
4.42c
5.84b
6.9a
Biol. value#

69.9c
78.6b
80.0ab
84.4a
ab,c Means within rows without common superscripts differ at P<0.05
# N retention as % of N digested

Figure 2. Effect of water spinach on DM digestibility in goats fed urea-treated
cassava stems with or without a supplement of biochar

SEM

p

0.151
0.171
0.065
0.217
1.39

<0.001
<0.001
0.065
<0.001
<0.001

Figure 3. Effect of biochar on DM digestibility in goats fed urea-treated
cassava stems with or without a supplement of water spinach

The most dramatic effects of biochar supplementation were on N retention (Table 5; Figures 4 and 5) and the biological value of the protein

absorbed (calculated as the N retained as percent of N digested) (Figures 6 and 7). Biochar increased daily N retention by 46% on the diet of ureatreated cassava stems and by 21% when water spinach replaced half of the urea-treated cassava stems (Table 5). Comparable values for the
increases in biological value of the protein were 12 and 4%. Biochar provides essentially no protein (0.0037% CP in diet DM) 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 in absorption of amino acids. It is hypothesized that biochar promotes 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 adsorb 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”.

Figure 4. Effect of water spinach on N retention in goats fed urea-treated
cassava stems with or without a supplement of biochar

Figure 5. Effect of biochar on N retention in goats fed urea-treated cassava
stems with or without a supplement of water spinach

Figure 6. 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 7. Effect of biochar on N retention as % of digested N in goats fed ureatreated cassava stems with or without a supplement of water spinach

Conclusions
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%.

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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 microbial
growth resulting in an increase in synthesis and hence of absorption of amino acids.
We suggest that biochar functions as a “prebiotic” – facilitating the activity of beneficial microbial communities that enhance fermentation or
remove the effects of phytotoxins or mycotoxins.

Acknowledgments
This research is part of the requirement by the senior author for the degree of PhD at Hue University of Agriculture and Forestry, Hue University,
Vietnam. The authors acknowledge support for this research from the MEKARN II project financed by Sida; and the University of An Giang,
Vietnam.

References
AOAC 1990: Official methods of analysis. 15th ed. AOAC, Washington, DC
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 foliage. Livestock Research for Rural Development. Volume 29, Article #104. />/5/phuo29104.html
Inthapanya S, Preston T R and Leng R A 2016; Ensiled brewers’ grains increased feed intake, digestibility and N retention in cattle fed ensiled cassava root, urea and rice
straw with fresh cassava foliage or water spinach as main source of protein. Livestock Research for Rural Development. Volume 28, Article #20. />/2/sang28020.htm
Inthapanya S, Preston T R, Phung L D and Ngoan L D 2017: Effect of supplements of yeast (Saccharomyces cerevisiae), rice distillers’ by-product and fermented cassava
root on methane production in an in vitro rumen incubation of ensiled cassava root, urea and cassava leaf meal. Livestock Research for Rural Development. Volume 29, Article
#220. />Lehmann J 2007: A handful of carbon. Nature447, 143-144 />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 foliage. Livestock Research for Rural Development. Volume 24, Article #199. />Leng R A 2017 : Biofilm compartmentalisation of the rumen microbiome: modification of fermentation and degradation of dietary toxins. Animal Production Science Review
/>Minitab 2000: Minitab user's guide. Data analysis and quality tools. Release 13.1 for windows. Minitab Inc., Pennsylvania, USA.
Orosco J, Patiño F J, Quintero M J and Rodríguez L 2018 : Residual biomass gasification on a small scale and its thermal utilization for coffee drying. Livestock Research
for Rural Development. Volume 30, Article #5. />Phanthavong V, Viengsakoun N, Sangkhom I and Preston T R 2014 : Cassava pulp as livestock feed; effects of storage in an open pit. Livestock Research for Rural
Development. Volume 26, Article #169. />Phanthavong V, Viengsakoun N, Sangkhom I and Preston T R 2015 Effect of biochar and leaves from sweet or bitter cassava on gas and methane production in an in vitro
rumen incubation using cassava root pulp as source of energy. Livestock Research for Rural Development. Volume 27, Article #72. />Philavong S, Preston T R and Leng R A 2017: Biochar improves the protein-enrichment of cassava pulp by yeast fermentation. Livestock Research for Rural Development.
Volume 29, Article #241. />Preston T R 2015; The role of biochar in farming systems producing food and energy from biomass. In: Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon
Sequestration and Reversing CO2 Increase (Editor: Thomas J Goreau) CRC Press, Tayler and Francis Group, Boca Raton, Florida USA
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 foliage 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 foliage 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 foliage (Manihot esculenta Crantz) as basal diet.
Livestock Research for Rural Development. Volume 29, Article #137. />Struhsaker T T, Cooney D O and Siex K S 1997 Charcoal Consumption by Zanzibar Red Colobus Monkeys: Its Function and Its Ecological and Demographic Consequences.
International Journal of Primatology, 18: 61-72. doi:10.1023/A:1026341207045 />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. />
Received 16 March 2018; Accepted 27 April 2018; Published 1 May 2018
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Digestibility, nitrogen balance and methane emissions in goats fed cassava foliage and
restricted levels of brewers’ grains
Le Thi Thuy Hang, T R Preston1, Nguyen Xuan Ba2 and Dinh Van Dung2
Faculty of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam

1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
2 Hue University of Agriculture and Forestry, Hue University, Hue City, Vietnam

Abstract
Four “Bach Thao” goats (14 ± 2 kg) were fed fresh cassava foliage (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 foliage 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
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 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

Introduction
Cassava (Manihot esculenta) 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 et al 2000; San Thy and Preston
2001). Several reports have shown the benefits of the fresh foliage 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 (Thanh et al 2013) and ensiled cassava pulp-urea (Toum et al
2017; Binh et al 2017).
The use of fresh cassava foliage as the sole diet of goats was pioneered by Vor Sina et al (2017). Growth rates on a diet of fresh cassava
foliage were 65 g/day and were 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 a s 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 foliage
fed to growing goats. Proportions of ensiled brewers’ grains above (6%) and below (2%) the 4% level were compared to identify the
optimum level.

Materials and methods
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 foliage (sweet variety). The design was a Latin square (Table 1) with four treatments and four periods, each lasting 15 days (ten
days for adaptation and 5 days for collection of feces and urine).
Table 1. The layout of the experiment
Period

Goat 1
Goat 2
1
BG0
BG2
2
BG6
BG0
3
BG4
BG6
4
BG2
BG4

Goat 3
BG4
BG2
BG0
BG6

Goat 4
BG6
BG4
BG2
BG0

Animals and management
The goats were housed in metabolism cages made from bamboo, esigned 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 the experimental periods, and prior to the start of each
5-day collection period.
Feeds and feeding management
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, 175 kg 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.

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The foliage 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 2hprior to each feed, morning and afternoon. On rainy days the cassava foliage was harvested the day before feeding so as
to avoid excessive levels of moisture in the foliage. 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 foliage. Feed refusals were weighed every morning prior to giving the new feed. Samples of
each diet component were collected daily, stored at -18C, and bulked at the end of each period for analysis.
Analytical procedures
The sub-samples of feeds offered and refused, and 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 (1985).).
Nitrogen in urine and ammonia in rumen fluid were determined by the Kjeldahl method (AOAC 1990). The pH of the rumen fluid was
determined by using an electronic meter (Eco Testr pH2). The concentration of ammonia nitrogen in the rumen fluid was determined by
diluting 15 ml of ruminal fluid with 5 drops of concentrated H2SO4 and distilling and titrating the released ammonia by the standard
Kjeldahl procedure (AOAC 1990). 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).
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.C.
Gas emission measurement
At the end of each period the goats were confined individually in a gas-proof chamber (a bamboo frame covered with 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).
Statistical analysis
Data were analyzed with the General Linear Model option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of
variation were treatments, animals, periods and error.

Results and discussion
Composition of diet ingredients
The crude protein (CP) of the cassava foliage (leaf and petiole combined) was considerably lower than the value of 21% CP in DM reported
by Vor Sina et al (2016) where the leaf alone had 29% CP in DM and the petiole 9.6% in DM).
Table 2. Composition of diet ingredients (9.5% in DM)
DM, %
CP
NDF
Cassava foliage
21.9
12.6
47.0
Brewers' grain
23.7
26.4
36.8

ADF
39.1
26.6

Ash
7.77
5.37

pH
4.35

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 3 and Figure 1). The same trend was seen for change in live weight (Figure 2) and DM feed conversion (Figure
3).
Table 3. Mean values for feed intake, live weight gain and DM feed conversion in goats
fed cassava foliage supplemented with increasing levels of ensiled brewers’ grains
Treatment
SEM
p
BG0
BG2
BG4
BG6
DM intake, g/d
Cassava foliage
5.92
<0.001
441a
486b
540c
468b
Brewers’ grains

0.00
10.7
22.3
30.7
0.621
<0.001
6.33
<0.001
Total DM
441c
497b
562a
498b
% of DM intake
Brewers’ grains
0.00
2.15
3.97
6.16
Crude protein
13.9
14.0
13.5
14.6
LW gain, g/d
48.3
96.7
142
80.0
6.7

<0.001
DM feed conversion
10.2
5.48
4.02
6.66
0.79
<0.001
abc Values in the same row with different lower-case letters differ at p<0.05

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Figure 1. Effect of level of ensiled brewers’ grains on DM intake

Figure 2. Effect of level of ensiled brewers’ grains on live weight gain

Figure 3. Effect of level of ensiled brewers’ grains on DM feed conversion

Coefficients of apparent digestibility of crude protein and DM showed the same curvilinear trends as were recorded for DM intake, LW gain
and feed conversion, with maximum values when the ensiled brewers’ grains were approximately 4% of the diet DM (Table 4 and Figure 4).
Table 4. Mean values of apparent digestibility in goats fed cassava foliage
supplemented with increasing levels of ensiled brewers’ grains
Treatments
SEM
p
BG0
BG2
BG4
BG6

1.66
0.021
CP
62.4a
69.9b
72.7b
70.8b
DM
2.7
0.036
55.9a
67.2b
70.8b
65.5b
OM
1.052
0.001
53.0a
58.2b
66.c
56.6ab
NDF
57.8
67.4
70.6
63.0
4.34
0.248
a,b,c Values in the same row with different lower-case letters differ at p<0.05

Figure 4. Effect of level of ensiled brewers’ grains on apparent digestibility of DM and crude protein

Rumen parameters
All criteria of rumen fermentation showed linear decreasing trends as the level of ensiled brewers’ grains in the diet was increased (Table 5;
Figures 5 and 6). The probable explanation of this trend is the stimulus to eating, and therefore to rumen fermentation, following the offering
of fresh feed in the morning. Reduction in ammonia levels and protozoal numbers are the logical result of the decrease in pH due to the
increased rate of fermentation.
Table 5. Mean values for protozoa numbers, ammonia and pH in rumen fluid,
before and 4h after, offering fresh feed in the morning
Treatments
SEM
p
BG0
BG2
BG4 BG6
Before feeding
14.1
13.1
12.8
12.7 0.388
0.098
Protozoa, x10-5/ml

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NH3, mg/liter
pH
4h after feeding
Protozoa, x10-5/ml

NH3, mg/liter
pH

129a
7.35

123ab
7.35

112b
7.21

113b
7.35

4.64
0.081

0.006
0.039

0.02
15.8a 14.6ab 13.8b 13.3b 0.459
0.009
127a
114ab 111ab 95.9b 7.261
6.94a
6.85a
6.60b 6.34c 0.056 <0.001
ab,c, Means within rows without common superscripts differ at P<0.05

Figure 5. Effect of level of ensiled brewers’ grains on rumen
pH before and after offering new morning feed

Figure 6. Effect of level of ensiled brewers’ grains on rumen
ammonia before and after offering new morning feed

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 ensiled brewers’ grains in the diet (Table 6; Figures 7 and 8). 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 6. Mean values for N balance (g/day) in goats fed cassava foliage supplemented
with difference levels of Brewery grain
Treatments
Nitrogen
SEM
p
BG0
BG2
BG4
BG6
Nitrogen balance, g/d
Intake
0.153
<0.001
9.82c 11.1b
12.1a
11.6bc
Feces
3.75

3.36
3.35
3.49
0.159
0.491
a
b
ab
a
Urine
0.066
0.024
1.63
1.27
1.49
1.64
Nitrogen retention
g/d
0.286
0.002
4.44a 6.48b
7.27b
6.51b
% of N intake
2.19
0.013
45.6a 58.4b
60.2b
56.0b
1.66

0.013
% of N digested
72.6a 83.5b
82.8b
79.8b
a,b,c Values in the same row with different

lower-case letters differ at P<0.05

Figure 7. Effect of dietary level of ensiled
brewers’ grains on N retention

Figure 8. Effect of dietary level of ensiled brewers’ grains on
N retention as a percentage of N digested

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 level of brewers’ grains in the diet was increased (Table 7; Figure 9). The trend was similar to that reported when cassava foliage
was replaced by brewers’ grains in a fattening diet fed to cattle (Binh et al 2017: Toum et al 2017) ; however, the replacement rate in both
these cases was over a much wider range of brewers’ grains (eg: Figure 10), the proportion of cassava foliage was lower and the basis of the
diet was ensiled cassava pulp-urea.
Table 7. 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 minute periods
Treatments
SEM
p
BG0
BG2
BG4
BG6

CH4/CO2
0.003
0.013
0.026b
0.027b
0.031ab
0.042a
abc,

Means within rows without common superscripts differ at P<0.05

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Figure 9. Effect of increasing proportions of brewers’ grains
replacing cassava foliage on methane: carbon dioxide
ratio in mixed air-expired breath of the goats

Figure 10. Methane: carbon dioxide ratio in mixed air-expired breath of cattle
fed increasing proportions of brewers’ grains replacing cassava foliage in a
fattening diet based on cassava pulp:urea (from Toum et al 2017)

Discussion
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 foliage, 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 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 on this context their role is as a “prebiotic” enhancing the activities and
effectiveness of beneficial microbial communities.

Conclusions
Adding 4% of brewers’ grains to a diet of cassava foliage 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.

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 foliage. 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
Do H Q, Son V V, Thu Hang B P, Tri V C and Preston T R 2002 Effect of supplementation of ammoniated rice straw with cassava leaves or grass on intake,
digestibility and N retention by goats. Livestock Research for Rural Development. Volume 14, Article #29. />Ffoulkes D and Preston T R 1978 Cassava or sweet potato forage as combined sources of protein and roughage in molasses based diets: effect of supplementation with
soybean meal. Tropical Animal Production 1978, Volume3, Number 3 />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.
Minitab 2000 Minitab Software Release 16.0
Novak M and Vetvicka V 2008 Beta-glucans, history and the present: Immunomodulatory aspects and mechanisms of action. Journal of Immunotoxicology; 5: 47-57
San Thy and Preston T R 2001 Potential of cassava in integrated farming systems. Livestock Research for Rural Development. />/pres.htm
Preston T R and Rodríguez Lylian 2004 Production and utilization of cassava foliage for livestock in integrated farming systems. Livestock Research for Rural
Development. Vol. 16, Art. No. 28. />Thomas, D. and Schutze-Kraft, R1990 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 foliage on the performance of crossbred growing cattle. Tropical Animal Health and Production 42(1)
1-11. www.ncbi.nlm.nih.gov/pubmed/19521793
Toum K, Preston T R and Thâm Hô Tham 2017 Cassava (Manihot esculenta Cranz) foliage 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 Developmen
Trinh Xuan Thanh, Khuc Thi Hue, Nguyen Ngoc Anh and T R Preston 2013 Comparison of different forages as supplements to a basal diet of chopped cassava
stems for growing goats. />Van Soest P J and Robertson J B 1985 Analysis of forage and fibrous foods. A laboratory manual for animal science 613 Cornell University, Ithaca, New York.
Vor Sina, Preston T R and Thâm Hô Tham 2017 Brewers’ grains have a synergistic effect on growth rate of goats fed fresh cassava foliage (Manihot esculentaCrantz)

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as basal diet Livestock Research for Rural Development 29 (7) 2017 />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. />
Received 29 November 2017; Accepted 25 February 2018; Published 1 April 2018
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Effect of biochar on growth and methane emissions of goats fed fresh cassava foliage
Le Thi Thuy Hang, T R Preston1, Nguyen Xuan Ba2 and Dinh Van Dung2
Faculty of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam

1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
2 Hue University of Agriculture and Forestry, Hue University, Hue City, Vietnam

Abstract
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 foliage (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. 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.
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: brewers’ grain, feed conversion, forages, greenhouse gas

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 other species of livestock, eg: price of goat (for 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 foliage, that is traditionally thrown
away, or burned, causing environment pollution.!! ). This contrasts with the reports of Wanapat et al (1997) and Preston (2001) that cassava
foliage 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 of 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, it enhanced the growth rate and reduced
enteric methane emissions of cattle (Leng et al 2012) and goats (Binh et al 2018; Silivong et al 2016).
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.

Materials and methods
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.
Experimental design
Twelve growing male goats of the Bach Thao breed, with an initial body weight from 14 to 16 kg, and about 3.5 – 4.5 months of age, were
housed in individual cages (Photo1) and given a basal diet of fresh cassava foliage 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 random block 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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Photo 1. The elevated cages for the goats

Feeding and management
The cassava foliage was from a “sweet” variety planted in the University area. It was harvested after periods of re-growth of 2-3 months
and fed 2-3h after harvesting. During rainy days, the foliage was harvested the day before feeding to limit the effects of excessive moisture
on the foliage DM content. Harvesting was by hand-cutting the cassava stems at ground level then rejecting the lower 30cm of “hard” stem
(Photo 2). The foliage was presented to the goats by hanging it in bunches in front of the feed troughs.

Photo 2. The “hard” stem 30-40cm from the ground (red line on the left) was rejected. The rest of the
plant (red line on the right) was suspended in the pens for the goats to choose freely

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). 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 (Photo 3). Drinking water was freely available.

Photo 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 foliage was offered at 7:30 and 14:30, while the brewers’ grains 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.
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 foliage (offered and residues) was separated into stems and leaves (containing attached petioles) (Photo 4). Representative samples
of each component were stored at -18°C until they were analyzed.

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Photo 4. Collecting samples of residues of the cassava foliage

Eructed gas emissions and analysis
At the end of the experiment the goats were confined individually in a closed chamber (a bamboo frame covered with polyethylene plastic)
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).
Analytical procedures
Samples of feeds offered and refused were analysed for DM, crude protein (CP) and ash by AOAC (1990) methods. Neutral detergent fiber
(NDF) and acid detergent fiber (ADF) were determined by the methods of Van Soest et al (1991). The equivalent hydrogen cyanic acid
content (HCN) in leaves-petioles of fresh cassava leaves was determined as per AOAC (2016). Condensed tannins were determined by the
method of AOAC 955.35 (2016)
Statistical analysis
Data were analyzed with the General Linear Model option of the ANOVA program in the MINITAB software (Minitab 2000). 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.

Results
Composition of diet ingredients
The levels of crude protein in the cassava leaves and combined leaf-petioles (Table 1) were similar to those reported by Sina et al (2017).
The “equivalent HCN” values in the leaf-petioles (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 (90 days) had a much higher water retention capacity of 4.89.
Feed intake, growth and feed conversion
For all the growth criteria expected to be influenced by nutrient manipulation of the 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 (Table 2; Figures 1-3). By contrast, in terms of effects on the rumen fermentation the improvement (decrease in methane
production) was linear (Table 4; Figure 4).
Table 1. Composition of diet ingredients
DM
CP
%
Ash
Cassava foliage
28.1 13.7
6.8
Soft stem
26.8
5.4
10.9
Leaf
29.4 22.1
2.7

Brewers’ grain
28.1 29.5
5.4
Biochar (1)
89.6
76.9
Biochar (2)
95.7
69.7

% in DM
ADF
NDF
39.2
48.3
41.2
51.4
37.3
45.1
26.6
40.1
-

Tannin
2.99

HCN
ppm
115

WRC
ml/g

3.81
4.89

Table 2. Mean values for feed intake, changes in live weight and feed conversion in
goats fed increasing levels of biochar n a diet of fresh cassava foliage
Biochar, % in diet DM
SEM
p
0.000
0.363
0.856
1.29
Cassava foliage
544
560
623
572
18.2
0.16
Brewers' grains
19.5
20
22.5
21.4
0.88
0.07
Biochar

0
2.11
5.58
7.74
Total
19.2
<0.01
563b
582b
652a
601b
CP, % in DM
14.2
14.1
14.0
14.0
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
5.04
0.03
LW gain, g/d
100b
120ab
128a
111ab
FCR
5.66
4.88
5.1
5.39
0.19
0.083
ab Means without common superscript differ at p<0.05
FCR = DM consumed/weight gain

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Table 3. Mean values for the ratio methane: carbon dioxide in eructed
gases from goats fed cassava foliage supplemented with biochar
Biochar, % in diet DM
SEM
p
0.000
0.363
0.856
1.29

CO2, ppm
982
669
686
709
CH4, ppm
32.4
18.2
16.3
15.7
0.0006 <0.001
CH4/CO2
0.033a 0.028b 0.025c 0.02d
ab Means without common superscript differ at p<0.05

Figure 1. Curvilinear response of DM intake of goats to percent biochar in a
cassava foliage diet with the optimum level at about 0.8 % biochar in DM

Figure 2. Curvilinear response of live weight gain of goats to percent biochar in a
cassava foliage diet with the optimum level at about 0.8 % biochar in DM

Figure 3. Curvilinear response in DM feed conversion of goats according to percent biochar
in a cassava foliage diet with the optimum level at about 0.8 % biochar in DM

Figure 4. Linear reduction in methane:carbon dioxide ratio in eructed
gas of goats fed up to 1.3% biochar in a diet of cassava foliage

Discussion
Biochar quality
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 WHC bochar was fed, as compared with
the previous period with 3.81 WRC biochar (Figure 5) is an interesting unsubstantiated observation that merits further research relating to
the water retention capacity of biochar and its relative value as an additive in livestock diets.

Figure 5. 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)

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Growth and feed conversion
The 26% increase in growth rate from including 0.8% biochar in the diet of goats in the present experiment concurs with growth responses
observed in: (i) goats fed legume tree and cassava foliage (Silivong et al 2016) or foliages from sweet and bitter cassava varieties (Phuong
et al 2019); and (ii) in cattle fed cassava roots and cassava foliage (Leng et al 2012; Sengsouly and Preston 2016; Saroeun et al 2018).
Common to all these reports is the presence of cassava foliage and cassava roots as major components of the diet.
Both roots and foliage 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).

Conclusions
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.
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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Received 6 March 2019; Accepted 4 April 2019; Published 1 May 2019
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