INTAKE, DIGESTIBILITY, N RETENTION AND GROWTH PERFORMANCE IN GOAT FED BAUHINIA ACUMINATA PLUS CASSAVA ROOT CHIPS AS THE BASAL DIET
INTRODUCTION
Research by Silivong and Preston (2015) showed that the growth rate of goats fed foliage of the legume tree Bauhinia acuminata was increased by supplementation with fresh water spinach and biochar. The protein in water spinach is very soluble (Silivong and Preston, 2015) and it is thought that its role in improving the utilization of foliages of low digestibility, such as Bauhinia acuminata, is because the water spinach acts as a source of readily available nitrogenous compounds for rumen micro-organisms (Silivong and Preston 2015, 2016). The positive role of biochar as a supplement in ruminant diets is thought to reflect another feature of ruminant nutrition, namely as a support mechanism for biofilms that host consortia of micro-organisms facilitating the utilization of nutrients with major benefits for the process of rumen fermentation (Leng, 2014). In this role, it appears that biochar is acting as a “prebiotic”, by promoting synergism between nutrients and micro-organisms in the animal’s digestive system. A similar synergism appears to be the explanation for the beneficial effects on growth rates of cattle (Binh et al., 2017) and goats (Sina et al., 2017) of small proportions in the diet of brewers’ grains, a byproduct derived from the industrial brewing of beer. The research with goats (Sina et al., 2017) highlighted a major interaction between the effect of the supplementary brewers’ grains and the nature of the basal diet.
The improvement in growth rate due to addition of brewers’ grains was 130% when the basal diet was fresh cassava foliage but only 30% when the basal diet was water spinach (Sina et al., 2017).
The hypothesis that was tested in the present experiment was that goats fed foliage of the legume tree Bauhinia acuminata would respond positively in growth rate and feed conversion to a supplement of brewers’ grains, and that the degree of response would be greater when cassava foliage, rather than water spinach, was the complementary source of protein.
MATERIALS AND METHODS
Experimental treatments and design
The basal diet was fresh foliage from the legume tree Bauhinia acuminata fed ad libitum, supplemented with biochar (1% of diet DM) and cassava root chips (4% of diet DM).
The treatments in a 2×2 factorial arrangement were:
Source of protein-rich foliage:
- 30% of DM feed intake (Water spinach: WS) - 30% of DM feed intake (Cassava foliage: CF) Supplementary brewers’ grains:
- 4% of DM feed intake (Brewer’s grains: BG) - No supplement (No-BG)
In the digestibility study the design was a 4×4 Latin Square with 4 male goats and 4 periods each of 12 days: 7 days for adaptation and 5 days for collection of feed refusals, feces and urine.
The goats (local breed) weighed 15.5±0.65 kg and were 5-6 months of age. They were purchased from farmers around Luangprabang city. They were housed individually in metabolism cages made from bamboo (dimensions of width 0.8 m, length 0.9 m and height 1 m), designed to collect separately feces and urine. In the growth study the design was a Randomized Completely Block Design (RCBD) with 4 replications of the two factors in a 2×2 factorial design, with sixteen goats (balanced males and females) with initial body weight of 14.4 ± 1.45 kg and 5-6 months of age.
They were housed in individual pens made from wood and bamboo. In both studies, the goats were vaccinated against Pasteurellosis and Foot and Mouth disease and were de-wormed before the start of the experiment.
Feeding and management
In both studies: Foliages of Bauhinia acuminata and water spinach (Ipomoea aquatica) were collected daily from natural stands in and around the University campus. Cassava (Manihot esculenta Crantz) foliage was collected daily from a demonstration plot in the Department of Animal Science Farm. Cassava root was harvested from the demonstration plot in the department of Animal Science Farm. It was chopped into small pieces and exposed to sunlight for 48h to reduce the moisture to about 15%. Brewers’ grains were purchased from a brewery in Vientiane city. The biochar was produced by burning rice husks in a top lit updraft (TLUD) gasifier stove (Olivier, 2010). It was ground to a particle size that passes through a 1 mm sieve. The biochar was mixed with the cassava root chips and fed from a plastic bucket. Bauhinia acuminata foliage, water spinach and cassava foliage were hung in bunches above the feed trough. Fresh feeds were offered twice daily at 07:30 and 16:00h. Water was freely available.
Measurements Metabolism study
Live weight was recorded in the morning before feeding at the beginning and at the end of each period. Feeds offered, and refusals were collected daily during the 5 days of the collection period. Urine was collected in buckets with 20 ml of a solution of sulphuric acid to ensure a pH of less than 4 (10% sulphuric acid concentrate + 90% distilled water). Feces and urine were collected daily and stored in the refrigerator (4-8ºC) until the end of each period, when sub-samples were mixed together.
Growth study
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 daily. Refusals were collected from individual animals every morning before offering new feed. Samples of Bauhinia acuminata, water spinach and cassava foliage (offered and residues) were separated into stems and leaves (containing attached petioles). Representative samples of each component were stored at -18°C until they were analysed. Samples of rumen fluid were taken on the last day of the experiment, using a stomach tube.
Chemical analyses
The samples of feeds offered and refused were analysed for DM, NDF, ADF, N and ash according to AOAC (1990) methods. The pH of rumen fluid was measured with a digital pH meter, prior to addition of sulphuric acid for subsequent analysis of ammonia by steam distillation (AOAC, 1990) and VFA by high pressure liquid chromatography (Water model 484 UV detector; column novapak C18; column size 3.9 mm x 300 mm; mobile phase 10 mM H2 PO4 [pH 2.5]) (Samuel et al., 1997). Solubility of the protein in the diet components was determined by extraction with M NaCl (Whitelaw et al., 1961).
Statistical analysis Metabolism study
The data were analyzed by the general linear model (GLM) in the ANOVA program of the Minitab software (Minitab, 2014).
The statistical model used in the digestibility study was:
Yijk = μ + Ti + Pj + Ak + eijk
In where, Yijk = Dependent variables., μ = Overall mean., Ti = Treatment effect (i=1-4)., Pj = Column effect (j=1-4)., Ak = Row effect (k=1-4)., eijk = Random error
Growth study
The statistical model was:
Yijk = μ + Bk + Pi + Aj + P i*Aj+ eijk
Where: Yijk is dependent variables., μ is overall mean., Bk is the effect of live weight., Pi is the effect of foliages source (water spinach and cassava foliage)., Aj is the effect of brewers’ grains source., (P*A)ij is the interaction between source of foliages and source of brewers’ grains and eijk is random error
RESULTS
Chemical composition of diet components
The low values for solubility of the protein in the leaves of Bauhinia acuminata and cassava, and the high values for the leaves of water spinach (Table 2), are in agreement with previous observations (Silivong and Preston, 2016) and are assumed to reflect different levels of tannin-rich compounds in the leaves of all three species.
Table 2. Chemical composition of dietary ingredients (% in DM, except DM which is on fresh basis)
DM N*6.25 Ash Protein solubility, % NDF ADF
Bauhinia leaves 40.0 15.0 21.2 23.7 43.7 32.4
Bauhinia stem 38.1 12.3 4.29 - 42.7 31.5
Cassava leaves 32.1 22.2 4.48 31.4 48.7 34.4
Cassava petiole 16.8 16.7 6.39 - 48.3 38.6
Cassava root chips 82.4 2.81 2.23 - - -
Water spinach 8.16 18.3 9.74 69.4 42.3 33.3
Brewers’ grains 28.7 27.2 38.1 - 40.7 29.5
Biochar - - 38.3 - - -
Metabolism study
The two factors had contrasting effects on digestibility of DM and on daily N retention (Table 3). Supplementation with brewers’ grains increased the digestibility of DM but the effect was more pronounced when cassava foliage was the source of additional protein as compared with water spinach. Daily N retention was similar for both foliages in the absence of brewers’ grains but, when brewers’ grains were added, N retention was greater with cassava than with water spinach.
Table 3. Mean values of apparent digestibility and N balance in goats fed Bauhinia acuminata supplemented with water spinach or cassava foliage, with (BG) and without (No-BG) brewers’ grains
Items
CF WS SEM p
No-BG BG No-BG BG SEM SEM
Foliage*BG P Foliage P BG P Foliage*BG Apparent digestibility, %
DM 68.4 74.9 69.9 72.3 0.60 0.86 0.558 <0.001 0.035
N balance, g/day
Intake 14.0 14.8 13.8 14.1 0.45 0.63 0.474 0.414 0.619
Feces 4.8 3.8 4.7 4.5 0.34 0.48 0.545 0.199 0.393
Urine 2.9 2.3 2.5 2.2 0.28 0.40 0.47 0.245 0.715
Retention 6.28 8.78 6.64 7.48 0.25 0.35 0.208 <0.001 0.037
N retention as:
% N intake 44.8 59.5 48.2 53.0 1.80 2.54 0.555 0.002 0.073
% N digested 68.6 79.2 73.0 78.1 2.12 2.99 0.585 0.022 0.368
BG: Brewer’s grain, CF: Cassava foliage, d: day, g: Gram, No-BG: Non-Brewer’s grain, P:
Probability value, SEM: Standard error of the mean with dferror: 0, WS: Water spinach Growth study
The Bauhinia acuminata foliage accounted for two thirds of the total DM consumed (Table 4).
Other components were in similar proportions in each of the diets, except for the brewers’ grains which was slightly higher (5% of diet DM) compared with the planned level of 4% of diet DM.
Addition of the brewers’ grains resulted in a small increase in diet crude protein content from 13.6 to 14.2% and from 13.8 to 14.5%, for the cassava foliage and water spinach treatments, respectively.
Table 4. Mean values of feed intake by goats fed Bauhinia acuminata plus cassava root chip supplemented with water spinach or cassava foliage and/or brewer’s grain
Items
CF WS SEM p
No-BG BG No-BG BG SEM SEM Foliage*BG P Foliage P BG P Foliage*BG DM intake, g/d
Bauhinia 395 403 380 384 1.94 2.74 <0.001 0.026 0.483
Water spinach - - 171 171 0.39 0.55 - 0.988 0.988
Cassava foliage 49 54 - - 0.43 0.60 - - -
Brewer’s grain - 0.8 - 1.5 0.12 0.16 0.045 - 0.045
Cassava root chip 1.6 2.5 2.2 2.3 0.10 0.14 0.130 <0.001 0.009
Biochar 7.9 8.1 8.0 8.1 0.02 0.03 0.130 <0.001 0.009
Total, g/day 583 628 591 627 2.55 3.61 0.375 <0.001 0.221
DM intake g/kg LW 34.4 35.2 34.0 35.6 0.10 0.15 0.911 <0.001 0.010 BG: Brewer’s grain, CF: Cassava foliage, d: day, g: Gram, Kg: Kilogram, LW: Live weight, No-BG:
Non-Brewer’s grain, P: Probability value, SEM: Standard error of the mean with dferror: 9, WS: Water spinach
There was an interaction between the effects of the two dietary factors on DM intake, growth rate and DM feed conversion (Table 5). When the protein-rich foliage was from cassava, the supplement of brewers’ grains increased the DM intake and the growth rate and improved the feed conversion but did not affect these criteria when the supplementary protein source was water spinach. This result is in line with the findings of Sina et al., 2017 who supplemented brewers’
grains (5% of diet DM) to goats fed fresh cassava foliage or water spinach, as the sole diet. In that study there was a 129% increase in live weight gain when brewers’ grains were added to cassava foliage, compared with only 25% improvement on the water spinach diet.
Table 5. Mean values for live weight, live weight change, DM intake and DM feed conversion for goats fed Bauhinia acuminata supplemented with cassava or water spinach foliage, with or without brewers’ grains (interaction effects)
Items
CF WS SEM p
No-
BG BG No-
BG BG SEM SEM
Foliage*BG P
Foliage P BG P
Foliage*BG Live weight, kg
Initial 14.4 14.5 14.5 14.4 0.39 0.54 0.893 0.822 0.964
Final 20.7 20.9 20.1 21.4 0.59 0.83 0.826 0.134 0.378
Daily gain, g/day 58 83 68 75 2.61 3.69 0.858 0.001 0.032
DM intake, g/kg LW 34.4 35.2 34.0 35.6 0.10 0.15 0.911 <0.001 0.010
DM feed conversion 10.1 7.6 8.8 8.4 0.19 0.27 0.397 <0.001 0.002
BG: Brewer’s grain, CF: Cassava foliage, d: day, g: Gram, Kg: Kilogram, LW: Live weight, No-BG:
Non-Brewer’s grain, P: Probability value, SEM: Standard error of the mean with dferror: 9, WS: Water spinach The higher values for rumen ammonia on the diets with water spinach (Table 6) were to be expected in view of the greater solubility of the protein in water spinach compared with cassava foliage (Table 2). However, on all diets, ammonia levels were sufficiently high to support normal rumen function. On each foliage source, rumen ammonia values were higher when brewers’ grains were included in the diet. There were minor differences in molar proportions of the VFA, and the Ac:Pr ratio, apparently related to the treatments; however, the small order of magnitude of the differences means they are unlikely to be of importance in relation to animal performance.
Table 6. Molar VFA proportions in rumen fluid from goats fed Bauhinia acuminata supplemented with water spinach or cassava foliage, with and without brewers’ grains
Items
CF WS SEM p
No-BG BG No-BG BG SEM SEM
Foliage*BG P
Foliage P BG P
Foliage*BG Molar %
Acetic 65.55 64.93 66.28 64.85 0.20 0.28 0.263 0.003 0.174
Propionic 24.83 23.50 24.08 24.60 0.21 0.29 0.56 0.196 0.008
Butyric 9.63 11.58 9.65 10.80 0.05 0.07 <0.001 <0.001 <0.001
Ac:Pr ratio 2.64 2.76 2.75 2.64 0.03 0.04 0.862 0.949 0.017
Rumen pH 7.06 7.05 6.99 6.90 0.02 0.03 0.01 0.166 0.233
NH3, mg/liter 186 194 215 232 1.31 1.85 <0.001 <0.001 0.003
BG: Brewer’s grain, CF: Cassava foliage, NH3: Ammonia, No-BG: Non-Brewer’s grain, P:
Probability value, pH: Percentage of Hydrogen Ion, SEM: Standard error of the mean with dferror: 9, VFA:
Volatile Fatty Acids, WS: Water spinach
DISCUSSION
We propose that the interaction in the degree of improved animal performance, according to whether the brewers’ grains were added to the diet with cassava foliage, compared with the diet containing water spinach, was because the brewers’ grains act as a prebiotic when included in diets containing potentially toxic elements such as the cyanogenic glucosides present in cassava foliage.
A similar explanation can be applied to the effects of “Kilao” (the byproduct from the fermentation/distillation of “rice wine”) in increasing growth and feed conversion of cattle fed ensiled cassava root and cassava foliage (Sengsouly and Preston, 2016). The improved performance appears to be manifested by increased diet digestibility and improved biological value of the digested protein. The greater response to brewers’ grains when cassava foliage was fed, compared
with water spinach, could be because of enhanced capacity to detoxify the cyanogenic glucosides present in cassava foliage as reported by Binh et al., 2017.
CONCLUSIONS
- Supplementing growing goats with brewers’ grains (5% of diet DM) increased diet digestibility and the biological value of the absorbed protein, resulting in improvement of live weight gain of 44% and in DM feed conversion of 25% when the basal diet was a legume tree foliage (Bauhinia acuminata) and the protein supplement was cassava foliage. Comparable data when water spinach was the protein supplement were relative improvements of 11 and 5%.
- It is proposed that brewers’ grains, a fermented byproduct from brewing “beer”, act as a prebiotic when added to a diet containing potentially toxic elements such as the cyanogenic glucosides present in cassava foliage.