Brewers’ grains have a synergistic effect on growth rate of goats fed fresh cassava foliage (Manihot esculenta Crantz) as basal diet

Vor Sina, T R Preston¹ and Thâm Hô Tham²

Center for livestock and Agriculture Development (CelAgrid). P O Box 2423, Phnom Penh Capital, Cambodia
sina_vor@yahoo.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
² Department of Animal Sciences, College of Agriculture and Applied Biology, Can Tho University Campus, Can Tho city, Vietnam

Abstract

Digestibility, N retention,  growth and feed conversion were measured in growing goats (n=12) housed in individual pens and fed basal diets of fresh sweet cassava foliage or fresh water spinach supplemented or not with a  low level (5-6% of diet DM) of ensiled brewers’ grains. The design was a 2*2 factorial with 3 replications. The brewers’ grains were fed at between 5 and 6% of the DM of the diet. The forages were given ad libitum.

There were major interactions between the effects of brewers’ grains supplementation and the nature of the basal diet. growing goats. In the absence of brewers' grains, growth, feed conversion, digestibility and N retention in performance were better when the  goats were fed water spinach; however, when brewers' grains were included in the  diets, performnance attributes all favored the diet of cassava foliage. Urine excretion of thiocyanate in the goats fed the cassava foliage diet was reduced by brewers’ grain supplementation; there was no thiocyanate in the urine of the goats fed water spinach. The results show that small amounts of brewers’ grains (5-6% of diet DM) confer major benefits on growth performance and health (expressed in the decreased urine excretion of thiocyanate) of goats fed cassava foliage as the sole diet.

Key words: digestibility, feed conversion, HCN toxicity, methane, N retention, thiocyanate

Introduction

In Cambodia, goat production is still limited when compared with other forms of livestock production. Farmers in upland areas are familiar with goat raising as a traditional source of meat for celebrations or family consumption. Usually, goat production is practiced in the traditional management system, in which the goats are released for day-time g razing and are housed in a pen with raised floors at night-time.

Similar with other developing countries in the region, small ruminants in Cambodia depend on natural pasture and crop residues. These are of low digestibility and usually imbalanced in essential nutrients which contribute to low feed intake. Supplements are required to improve rumen microbial fermentation and therefore the performance of the host animals.

In Cambodia, cassava (Manihot esculenta) is usually planted with the main purpose of root harvesting and the leaves are left in the field. It has been shown that this residue can be a valuable source of protein for feeding to many kinds of animals (Preston 2001). Early work with freshly chopped cassava foliage (leaves, petioles and stems) showed that it could be the sole source of supplementary protein and roughage in diets for fattening cattle based on liquid molasses-urea (Ffoulkes and Preston 1978). Benefits from feeding cassava foliage to goats were: a curvilinear increase in N retention when it replaced grass as the supplement to ammoniated rice straw (Do et al 2002); a linear response in milk production when increasing quantities of cassava foliage were added to a diet of ammoniated rice straw and chipped cassava root (Dung et al 2010); and a reduction in fecal nematode egg counts when cassava foliage replaced grass as the main diet (Seng Sokerya and Preston 2003).

Brewers’ grains are the solid residue left after the processing of germinated cereal grains (malt) for the production of beer (Mussatto et al 2006), Though barley is the main grain used for brewing, beers are also made from wheat, maize, rice, sorghum and millet. In the brewing process, grains are soaked in water until they germinate and then dried to produce the malt (malting). The malted grains are milled and steeped in hot water so that enzymes transform the starch into sugar. The resulting sugar-rich liquid is then boiled, filtered and fermented to produce beer. Brewers’ (spent) grains, collected at the end of the mashing process, represent about 20% by dry weight of the original grain (Mussatto et al 2006).

Brewers’ grains have a long history in animal feeding. Before the industrial revolution, farms and monasteries in Europe brewed their own beer and fed their livestock with the resulting by-products. These practices changed with the industrialization of brewing and animal feeding and brewers’ grains began to be used by the feed industry (Crawshaw 2004).

Recently, brewers’ grains have been the main source of bypass protein in a diet of cassava pulp-urea and restricted rice straw fed to fattening cattle (Phanthavong et al 2016). A follow-on from this experience was the observation that brewers’ grains appeared to have “prebiotic” characteristics as when fed at very low levels (4% of diet DM) they reduced the apparent toxicity of a “ bitter” variety of cassava, when this was fed to cattle as the sole source of protein and fiber in the cassava-pulp-urea diet (Binh et al 2017). The apparent “prebiotic” effect of the brewers’ grains was reflected in a 100% reduction in urinary excretion of thiocyanate (the detoxification product of hydrocyanic acid that is produced when bitter cassava foliage is chewed in the process of eating) and resulted in an increase in growth rate of the cattle from 60 to 500 g/day (Binh et al 2017).

The hypothesis that was tested in the present experiment was that similar low levels of brewers’ grains (4% of diet DM) would have a beneficial effect on growth of goats fed cassava foliage as the sole diet. For comparison, the brewers’ grains supplement was fed with fresh water spinach foliage, a feed that does not contain cyanogenic precursors.

Materials and methods

Location

The experiment was carried out in the Center for Livestock and Agriculture Development (CelAgrid), located about 25km south of Phnom Penh, Cambodia. Mean daily temperature during the experiment ranged from 26°C to 38°C.

Experimental animals and housing

Twelve male goats of local breed with average body weight of 13.2 ± 0.9 kg (4 to 5 months of age) were selected from a farmer flock (Photo 1). They were de-wormed using Ivermectin and housed in individual cages (1mx 1.5m) with bamboo floors in an open-sided, roofed shed (Photo 2).

Photo 1. Local goats were selected from a farmer‘s flock	Photo 2. Individual pens made from bamboo

Treatment and experiment design

The experiment was arranged as a 2*2 factorial with 4 treatments and three replications.

The factors were:

Foliage source

WS: Fresh water spinach

CF : Fresh cassava foliage

Brewers’ grains

BG: Brewers’ grains (5-6% in diet DM)

No BG: Without brewers’ grains

Diets and feeding

The cassava foliage (sweet variety) was harvested after 4 months of re-growth (Photo 3). Water spinach was collected from a site near the center (Photo 4). The cassava foliage and water spinach were fed ad libitum by hanging the foliage above the feed trough (Photo 5), fresh material being offered at 8:00, 12:00 and 18:00.h Fresh brewers’ grains (Photo 6) were fed two times per day (8:00 and 12:00h) at a level of 5% of the recorded intake on the previous day (DM basis).

Photo 3. Cassava foliage ready for harvesting (background)	Photo 4. Harvesting water spinach
Photo 5. Hanging the foliage above the feed trough	Photo 6. Brewers’ grains

Data collection and chemical analysis

Feed consumption was recorded by collecting refusals from individual animals every morning before offering new feed. The goats were weighed in the morning before feeding every ten days. On the penultimate day of the experiment, urine was collected for analysis of thiocyanate using the procedure developed by Haque and Bradbury (1999) (Photos 7 and 8).

The DM, ash and nitrogen in feed offered were determined according to AOAC (1990); neutral detergent fiber (NDF) and acid detergent fiber (ADF) were measured using the procedure of Van Soest et al (1991). The pH of the brewers’ grains was measured with an electronic pH meter fitted with a glass electrode. 

Data analysis

Experimental data were analyzed with the Generalized Linear Model (GLM) option of the ANOVA program in the MINITAB software (Minitab 2000). Sources of variation were: forage source, brewers’ grain supplement, interaction brewers’ grain * forage source and error.

Results

Composition of feeds

The crude protein in the cassava foliage was lower than that in brewers’ grains and higher than in water spinach (Table 1).

Feed intake

DM intake was 14% greater when cassava foliage rather than water spinach was the basal unsupplemented diet (Table 2; Figure 1). Suppplementation with  brewers' grains increased the DM intake by 47 % on the  cassava diet and by 13% when the basal diet was water spinach.

Leaves were eaten by preference (86-87%) when the foliage was from cassava; the leaf fraction consumed for water spinach was much lower (56-57%) (Table 3).

Figure 1. Brewers’ grains (BG) increased DM intake more when the basal diet was cassava foliage than when it was water spinach.

Growth rate and feed conversion

Growth rates were uniform over the 70 day experimental period (Figure 3).

Figure 2. Growth curves of goats fed basal diets of cassava foliage (CF) or water spinach (WS) with and without a supplement of brewers’ grains (BG) at 4% of diet DM

There was an interaction between the basal diet and the effect of the supplementary brewers’ grains on growth rate (Figure 3) . Without brewers’ grains growth rate was 43% greater on the water spinach diet than on cassava (Table 4): however, when brewers’ grains were included in the diet the opposite effect occurred with growth being 24% greater for goats fed the cassava diet. The symbiotic effect of the brewers’ grains is apparent in the major improvements in growth rate and DM feed conversion of 130% and 41%, respectively, when brewers’ grains were added to the cassava foliage dies; the improvements  were much less (30% and 20%) when brewers' grains were added tot the water spinach diet (Table 4; Figures 4 and 5).

Figure 3. Brewers’ grains (BG) increased LW gain by 130% when the basal diet was cassava foliage and by 30% when the basal diet was water spinach

Figure 4. Brewers’ grains (BG) improved DM feed conversion in goats by 41% when the basal diet was cassava foliage and by 20% when the basal diet was water spinach

Digestibility and N retention

There were interactions between the basal diets and the effects of supplementation with brewers’ grains (Tables 5 and 6; Figures 6 and 7). Improvements in digestibility due to supplementation with brewers’ grains were much greater when the basal diet was cassava foliage than when it was water spinach). In the absence of brewers’ grains, apparent digestibility were higher for water spinach than for cassava foliage.

Figure 5. Brewers’ grains increased DM digestibility on the cassava foliage diet but not on the water spinach diet

Brewers’ grains increased N retention by 150% on the diet of cassava foliage but by only 35% on the water spinach diet. In the absence of brewers’ grains the N retention was higher for water spinach than for cassava foliage (Table 6; Figure 6). As expected there was a close relationship between N retention and live weight gain (Figure 8).

Figure 6. Brewers’ grains increased N retention by 150% on the diet of cassava foliage but by only 35% on the water spinach diet.

Figure 7. There was a close relationship (R=0.99) between daily N retention and live weight gain

Urine thiocyanate

Excretion of thiocyanate in the urine of goats fed cassava foliage was reduced by brewers’ grains (Table 7). As expected, thiocyanate was not detected in the urine of the goats fed water spinach.

Discussion

The positive effects of a small supplement of brewers’ grains (5-6% of diet DM) on feed intake, growth and feed conversion of goats fed cassava foliage, are similar to those reported in cattle by Binh et al (2017). The difference between the two experiments was that: in the present experiment the cassava foliage was of a sweet variety and constituted all or 95% of the diet; while in the experiment of Binh et al (2017) the cassava foliage was of a “bitter variety and provided only 25-30% of the diet DM, the remainder being cassava root pulp and urea. The beneficial effect of the brewers’ grains in reducing the degree of toxicity of the cyanogenic glucosides present in cassava foliage, reflected in the reduced rate of excretion of thiocyanate in the urine, was a common response in both experiments. The lower concentration of cyanogenic glucosides in the foliage of sweet, as opposed to bitter, cassava varieties (Phuong e al 2015), would have been offset by the higher level of cassava foliage (96-100% of the diet) in the present experiment compared to the 20-30% level of bitter cassava foliage in the diets used by Binh et al (2017).

In the report of Binh et al (2017) it was hypothesized that the effect of the brewers’ grains might have been because of the presence of ß-glucan in the cell walls of barley (the cereal grain from which brewers' grains is derived) and/or in yeast (also present in the brewers' grains; Musatto et al 2006); and that the ß-glucan may act by providing support for rumen biofilms (Leng 2014), with resultant benefits in “habitat” for micro-organisms that detoxify the HCN produced in the rumen when animals consume cassava foliage.

Conclusions

• There were major interactions between the effects of brewers’ grains supplementation (5-6% of diet DM) and the nature of the basal diet (cassava or water spinach) on growth, feed conversion, digestibility and N retention in growing goats.
  
  
• In the absence of brewers' grains supplementation, performance attributes were better when the goats were fed water spinach; however, when 5% of brewers' grains were included in the diets, performnance attributes all favored the diet of cassava foliage.
  
  
• Urine excretion of thiocyanate in the goats fed the cassava foliage diet was reduced by brewers’ grain supplementation; there was no thiocyanate in the urine of the goats fed water spinach.
  
  
• The results of the present experiment confirm that, in some way or other, small amounts of brewers’ grains confer major benefits on growth performance and health (expressed in the decreased urine excretion of thiocyanate) of ruminants fed cassava foliage as the sole diet.

Acknowledgements

This research was done by the senior author as part of the MSc degree in Animal Production "Improving Livelihood and Food Security of the people in Lower Mekong Basin through Climate Change Mitigation" in Cantho University, Vietnam. The author expresses gratitude to the MEKARN II project, supported by Sida, for financial support for this research; to Dr Chhay Ty who provided valuable help in analysis; to the students from the Royal University of Agriculture (RUA) who helped in the feeding and management of the goats; and to the Center for Livestock and Agriculture Development (CelAgrid) for providing the facilities to carry out the experiment.

References

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Received 17 March 2017; Accepted 25 May 2017; Published 2 July 2017

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