Effects of a supplement of yeast-fermented broken rice on nitrogen retention and methane emissions in growing goats fed Para grass (Brachiaria mutica)

Nguyen Thi Thu Hong^1,2, Nguyen Thi Ngoc Trang³ and Le Tran Minh Hieu^1,2

¹ An Giang University, An Giang, Vietnam
ntthong@agu.edu.vn
² Vietnam National University Ho Chi Minh City, Vietnam
³ Faculty of Natural Resources - Environment, Kien Giang University, Vietnam

Abstract

Growing goats fed a basal diet of Para grass (Brachiaria mutica) responded to a supplement of yeast-fermented broken rice with increased growth rate as measured by nitrogen retention and with an enriched rumen fermentation characterised by increasing proportions of propionic acid which in turn lead to reduced emissions of methane.

Keywords: rumen fermentation, propionic acid, Saccharomyces cerevisiae

Introduction

Goats production plays an important role for the livelihood of farmers in rural areas (Steinfeld et al 2006). More so, they could easily be integrated into different farming systems because of their small body size compared to cattle (Hirpa and Abebe 2008). In tropical regions, production systems based on natural grass or rangelands may lead to poor animal performance (Alexandre and Mandonnet 2005). Improving animal performance is the most efficient way to increase food production to meet human needs without increasing land use and greenhouse gas emissions (Solaiman 2010). To effectively develop goat herds in condition of natural food sources shortage due to land limitation, households not only have to improve quality of goat breeds, the caring and nurturing methods, but they should also take efficiency the advantages of available green food sources in adding to rations for reducing production costs and increasing profits for farmers.

Climate change can lead to serious impacts on production, life and environment (Watson 2008). Methane mitigation in ruminants is possible through various strategies (Martin et al 2010). Choosing the most appropriate livestock system, taking advantage of adaption to climate of these species and local feed sources, improving feed conversion and reducing amount of feed consumed per unit of product are effective methods to reduce greenhouse gas emissions and increase profitability of production (Johnson and Johnson 1995).

Anaerobic fermentation of polished rice with yeast (Saccharomyces cerevisiae) has been shown to produce a feed supplement that reduced methane production in an in vitro rumen incubation of a diet of cassava pulp, urea and cassava foliage hen added at 4% (DM basis) of a normal diet (Sangkhom et al 2020a The method is a simple and easily done under farm conditions. The description of the system is that polished rice (as prepared for human consumption) is soaked in water (1 kg rice: 0.5 kg water) for 30 minutes and then milled in a liquidizer, prior to adding yeast (Saccharomyces cerevisiae) at 3% (DM basis). The mixture is then put in closed plastic bags and allowed to ferment for 7 days prior to being evaluated for its effect on methane production in an in vitro rumen incubation of a typical diet designed for growing cattle (Sangkhom et al 2020b). The yeast-fermented rice (YFR) was included in the diet at the rate of 4% (DM basis).

The objective of the present study was to test the effect of a supplement of yeast-fermented broken rice (YFR) on rumen fermentation, methane emissions and nitrogen retention in growing goats fed a basal diet of Para grass (Brachiaria mutica).

Material and methods

Location

The experiment was carried out in the farm of An Giang University from February to June 2022.

Animal, experimental design and diet

Four male Bachthao goats, 5 months old and 15.9 kg body weight were housed in individual cages (1.0m×0.9m×1.2m) and fed a basal diet of Para grass (Brachiaria mutica).

The goats were allocated to a 4x4 Latin square design with 4 treatments. The treatments were yeast-fermented broken rice fed at 0. 5, 10 and 15% of the diet DM (YFBR 0. YFBR5. YFBR10 and YFBR15) corresponding to the yeast-fermented broken rice replacing para grass (Brachiaria mutica) at the levels of 0; 5; 10 and 15% (DM basis).

The goats were vaccinated against foot and mouth disease and de-wormed before the start of the experiment. They were individually fed in metabolism cages with free access to water and mineral blocks. New feed was offered daily at 08:00 and 16:00.

Broken rice was soaked in water (1kg broken rice; 1 liters water) for 5 hours and wet-milled in a liquidizer. Yeast (Saccharomyces cerevisiae) was added (5g yeast to 1kg broken rice) and the mixture enclosed in a plastic bag for anaerobic fermentation during three days.

Sampling and measurements

Each experimental period lasted 20 days. For the first 10 days in each period, the goats were adapted to the new diets. From 11 to 15 days feces and urine were collected, and feeds offered and refused were recorded. There was a rest periods of 5 days between experimental periods, when the goats were feed only grass.

Samples of feeds, refused and feces were pooled over the 5-day collection period. Samples were first dried in a forced-air oven at 60°C for 48 h and then ground to pass a 1-mm screen and refrigerated (-18°C) prior to analysis. The urine was acidified with 10% H₂SO₄ to prevent ammonia-N loss.

On the 15th day of each period of the experiment, the carbon dioxide and methane in eructed gases were measured. The gases were collected in the morning by placing the goats in a glass chamber and after a period of 5 minutes for equilibration with the air in the chamber, the concentrations of methane and carbon dioxide were determined using CH₄ meter SPD203 and CO₂ meter AQ-9901SD Lutron. The rumen fluid samples were collected at 3h post morning feeding using a stomach tube. The rumen fluid was immediately determined pH value. The subsample was then filtrated through a clean double layer of cotton cloth, and the liquid fraction was acidified with 1M H₂SO ₄ (9:1 w/w), centrifuged at 10,000×g for 15 minutes and stored at −20°C for analyses of VFA and NH ₃-N concentrations.

Chemical analysis

The samples of feed offered and refused and of feces were analysed by AOAC (1990) methods for: dry matter (DM) by drying at 105⁰C for 24h; organic matter (OM) by ashing at 550⁰C for 4h; and crude protein (CP) by Kjeldahl technique. Neutral detergent fibre (NDF) and acid detergent fiber (ADF) were analysed using the method of Van Soest and Robertson (1985).

Ruminal pH was determined by a pH meter (Hanna HI2210-02). Rumen NH₃-N concentration was analyzed using the Kjeldahl methods (AOAC, 1990).

Concentrations of individual VFA were analyzed using a Thermo Trace 1310 GC system (Thermo Scientific, Waltham, MA, USA) equipped with a flame ionization detector. The inlet and detector temperature were maintained at 220°C. Aliquots (1 μL) were injected with a split ratio of 10:1 into a 30m × 0.25mm × 0.25μm Nukol fused-silica capillary column (Cat. No: 24107, Supelco, Sigma-Aldrich, St. Louis, MO, USA) with nitrogen carrier gas set to a flow rate of 1 mL/min and initial oven temperature of 80°C. The oven temperature was held constant at the initial temperature for 1 min, and thereafter increased at 20°C/min to a temperature of 180°C and held for 1 min, and increased at 10°C/min to a final temperature of 200°C, and a final run time of 14 min (Bharanidharan et al 2018). Individual VFA peaks were identified based on their retention times, compared with external acid standards including acetic, propionic and butyric acids. (Sigma-Aldrich, USA).

Results and discussion

Composition of diet ingredients and of the diets

Data on chemical composition of the feeds are presented in Table 1.

Intakes of dry matter, organic matter and crude protein were increased as yeast-fermented broken rice level was increased (Table 2). Similar effects on feed intake and digestibility, as yeast-fermented rice levels in the diets increased, were reported by Nguyen Van Thu et al (2022).

Figure 1. Supplementing a diet of Para grass with yeast fermented broken rice increase the nitrogen retention by growing goats

The proportion of propionic acid in the rumen VFA was increased Table 3 (Figure 2, whith corresponding reductions in emissions of methane (Figure 3), as the proportion of YFR in the diet was increased.

Figure 2. Supplementing a diary of para grass with yeast fermented rice level to increases in the propulsion of propionic acid in the rumen vfa of growing goats	Figure 3. Effect of yeast fermented rice supplement on the ratio of maintain to carbon dioxide in expired breath of growing goats

Conclusions

Growing goats fed a basal diet of Para grass (Brachiara mutica) responded to a supplement of yeast fermented broken rice with increased retention of nitrogen and with an enriched rumen fermentation characterised by increasing proportions of propionic acid which in turn lead to reduced emissions of methane.

Editorial note

The apparent discrepancy in these results reported here, and those described by Sangkhom et al (2020b can be explained by the lower level of yeast (0.5% in DM) in the initial fermentation compared with that used by Sangkhom et al (2020b) which was 3% of the rice DM.

The authors of this paper agreed to explore this issue by determining the effect of the level of yeast on the proportion of water_souble DM after completing the fermentation. The results (Figure 4) showed that there was a close relationship between the level of yeast added to the broken rice in the initial fermentation and the concentration of water-soluble DM in the fermented product. The percentage of water-soluble DM is the fermented rice reflects the degree to which the glucose polymrts (eg: Beta-glucan) in the yeast cell wall has been hydrolysed.

Figure 4. Relationship between level of yeast added to broken rice and its effect on the liberation of water soluble dry matter in the form of betaglucan and other glucose polymers

The solubility of the dry matter was determined by shaking 3 g of dried samples in 100 ml of 1M NaCl for 3h then filtering through Whatman No. 4 filter paper, and DM content of YFR on filter paper were analyzed by AOAC (1990) methods for dry matter by drying at 105⁰C for 48h.

The level of water soluble dry matter in the fermented rice is indicative of the concentration of Beta-glucan and other glucose polymers in the fermented rice which, when ingested by the animal, act as specialized sources of energy for the growth of bacteria that produce volatile fatty acids especially propionic and butyric acids.

To compensate for the reduced supply of glucose polymers, as a result of the lower level of yeast in the initial fermentation, it was necessary to increase the levels of YFR in the diet to a range of 0-15% instead of the 0-4% of the diet DM, which was the level used by Sangkhom et al 2020.

It is important in future research on YFR that the initial fermentation should be done with 3% of yeast on DM basis in the fermentation process to produce the YFR.

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