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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 Preston

1

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
%
0
1
2
3
4
SEM
p

Tannin

%
1.24
1.09
1.10
1.02
1.05
0.025
<0.001

HCN
mg/kg
80.2
65.8
61.4
63.1
59.8
0.699
<0.001

Ammonia

pH

0.04
0.64
0.80
0.90
1.09
0.006
<0.001

5.31
6.70
7.09
7.82
7.91
0.099
<0.001

NDF
%
63.8
61.7
60.8
59.8
59.8
0.147
<0.001

ADF
%
50.6
49.8
49.2
48.7
47.5
0.157
<0.001

CP

%
5.82
8.12
8.99
12.5
13.7
0.0615
<0.001

Table 2. Mean values for effects of storage time on composition of the ensiled cassava stems

Storage,
weeks
0
2
4
6
8
SEM
p

Tannin
%
1.24
1.18
1.02
1.04
1.01
0.025
<0.001

HCN
mg/kg
144
130
47
9.33
0.00
0.699
<0.001

Ammonia

pH

0.09
1.65
0.59
0.57
0.57
0.0058
<0.001

6.38
7.41
7.52
7.12
6.40
0.099
<0.001

NDF
%
65.6
61.0
60.0
59.7
59.6
0.147
<0.001

ADF
%
50.5
50.0
48.6
48.6
48.2
0.157
<0.001

CP
%
8.05
10.3
10.6
10.2
10.0
0.0615
<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
% urea in DM
DM, %

0.0
22.1

1.0
21.0

2.0
21.7

3.0
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. (20

th

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

7 of 8


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 Nretention in goats fed urea-treated cassava stems
1

2

Le Thi Thuy Hang, T R Preston , R A Leng and Nguyen Xuan Ba

3

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 ureatreated 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

1 of 5

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

Photo 2. Chopping into
5-10 cm lengths

Photo 3. Urea added at

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

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

3% of stem DM

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

o

sample of 10% of the urine was stored at -4 C for analysis of nitrogen (AOAC 1990); (ii) the feces were mixed and a
o

sample (10%) stored frozen at -20 C.
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
DM,
% in 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
a
a
b
ab
UCS
15.0
0.002
367
428

300
352
Biochar
0
3.84
0
3.91
Water spinach
0
0
159
163
b
ab
ab
a
Total
20.0
0.009
367
432
459
518
d
c
b
a
DMI, % LW
0.048
<0.001

2.27
2.59
2.83
3.12
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.
Dry matter (%)

UCS
b
59.4

UCSB
a
64.8

UCSW
b
60.8

UCSWB

a
66.3

b
a
a
a
Crude protein
53.2
60.1
59.3
63.1
b
a
ab
a
Organic matter
59.4
65.0
61.6
66.8
ab,
Means within rows without common superscripts differ at P<0.05

SEM
0.88

p
<0.001

1.54
1.78

<0.010
0.066

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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N balance, g/d
Intake
Feces
Urine
Retention
Biol. value#

UCS

UCSB

d

c

8.13

b
3.79

9.23

3.659

b

UCSW
12.4

b

a
5.099

UCSWB
a

13.0

4.81

a

SEM
0.151
0.171
0.065

0.217
1.39

1.30
1.17
1.42
1.25
d
c
b
a
3.03
4.42
5.84
6.9
c
b
ab
a
69.9
78.6
80.0
84.4
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

p

<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
urea-treated 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 microorganisms 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 Figure 7. Effect of biochar on N retention as % of digested N in goats fed ureaurea-treated cassava stems with or without a supplement of biochar
treated 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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Livestock Research for Rural Development 30 (4) 2018

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Digestibility, nitrogen balance and methane emissions in goats fed
cassava foliage and restricted levels of brewers’ grains
1

2

Le Thi Thuy Hang, T R Preston , Nguyen Xuan Ba and Dinh Van Dung

2

Faculty of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam



1Centro 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

o

sample of 10% of the urine was stored at -4 C for analysis of nitrogen (AOAC 1990); (ii) the feces were mixed and
o

a sample (10%) stored frozen at –20 C.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

ADF
Cassava foliage
21.9
12.6
47.0
39.1
Brewers' grain
23.7
26.4
36.8
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

BG0

Treatment
BG2

BG4

’ grains
BG6

SEM

p

DM intake, g/d
a
b
c
b
Cassava foliage
5.92
<0.001
441
486
540
468
Brewers’ grains
0.00
10.7
22.3
30.7
0.621
<0.001
c
b

a
b
Total DM
6.33
<0.001
441
497
562
498
% 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
p
Treatments
SEM
BG0
BG2
BG4
BG6
a
b
b
b

CP
1.66
0.021
62.4
69.9
72.7
70.8
a
b
b
b
DM
2.7
0.036
55.9
67.2
70.8
65.5
a
b
c
ab
OM
1.052
0.001
53.0
58.2
66.
56.6
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
p
Treatments
SEM
BG0
BG2
BG4
BG6
Before feeding
-5
14.1
13.1

12.8
12.7 0.388 0.098
Protozoa, x10 /ml

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

Protozoa, x10 /ml
NH3, mg/liter

pH

ab,c,

a
129
7.35
a

15.8
a
127
a

6.94

ab
123
7.35
ab

14.6
ab
114
a

6.85

b
112
7.21
b

13.8
ab
111
b

6.60

b
113
7.35
b

13.3
b
95.9
c

6.34

4.64

0.006

0.081

0.039

0.459
7.261
0.056

0.02
0.009
<0.001

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
SEM
p
Nitrogen
BG0 BG2
BG4
BG6
Nitrogen balance, g/d
c
b
a
bc
0.153 <0.001
9.82
11.1
12.1
11.6
Intake
3.75
3.36
3.35
3.49
0.159 0.491

Feces
a
b
ab
a
0.066 0.024
Urine
1.63 1.27
1.49
1.64
Nitrogen retention

a
b
b
b
g/d
0.286
0.002
4.44
6.48
7.27
6.51
a
b
b
b
% of N intake
2.19
0.013

45.6
58.4
60.2
56.0
a
b
b
b
% of N digested
1.66
0.013
72.6 83.5
82.8
79.8
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
CH4/CO2
abc,

BG0
b
0.026

Treatments
BG2
BG4
b
ab
0.027
0.031

BG6
a
0.042

SEM

p

0.003

0.013

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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