leaves of tropical trees (blue columns) Maselema D and Chigwa F C 2017
| Livestock Research for Rural Development 35 (8) 2023 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Tropical glasses produce four to five times as mall methane as the leaves of tropical trees (Figure 1). The challenge is to divert the energy that normally is emitted as methane so that it becomes productive net energy in the form of propionic acid which will facilitate utilisation of energy for productive purposes otherwise lost as methane which is a major contributor to global warming.
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| Figure 1.
Tropical grasses (green colours) produce four to five times
as much methane as the leaves of tropical trees (blue columns) Maselema D and Chigwa F C 2017 |
We discuss recent results on the feeding of yeast fermented rice (YFR) as a supplement that will increase the productivity of ruminant livestock and reduce emissions of methane.
We find that the level of the YFR is critical in order to optimise the effect of the supplement on the rumen fermentation. The results indicate that the level of YFR should not exceed 4% of the diet dry matter in order to optimise the effect of the supplementation on the rumen fermentation, and specifically the proportion of propionic acid in the rumen VFA. When higher levels of YFR are fed it results in reduced proportions of propionic acid in the rumen VFA and increased emissions of methane. As the formation of propionic acid require hydrogen this results in less hydrogen available for the reduction of carbon dioxide to form methane.
The related issue is why high level of YFR lead to reduced proportions of propionic acid in the rumen VFA? We suggest this could be the result of a too high level off Beta-gluca leading to the accumulation of lactic acid in the rumen.
Key words: Beta-glucan, global warming, lactic acid, propionic acid
The following series of events led to the development of a feeding system in which a low level of yeast-fermented polished rice facilitated a 20% improvement in in growth and feed conversion of ruminant livestock with correspond ing decreases in emissions of methane.
Brewers’ spent grains fed to growing cattle at 4% of the diet reduced the toxicity caused by feeding foliage from a bitter variety of cassava and improved the growth rate and feed conversion (Binh et al 2014).
The byproduct from the yeast fermentation of polished rice to make “rice wine” supported improvements in liveweight gain and feed conversion with reduced emissions of methane, when fed to growing cattle (Sangkhom et al 2017; Photo 1,2) .
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| Photo 1. Cassava root | Photo 2. Rice destillers byproduct | Photo 3. Cassava foliage, |
| The major ingredients in the diet (Sangkhom et al 2017) | ||
In addition, the process provided evidence as to why the byproducts from both large- and small-scale production of alcoholic drinks (beer and rice wine) could be the means to improve both ruminant livestock productivity as well as the environmental health of the planet by reducing emissions of methane.
The evidence is that yeast-based fermentation of carbohydrate-rich substrates produces both potable alcohol – beer and rice wine – and a by-product rich in polysaccharide such as Beta-glucan, derived from the hydrolysed cell walls of the “spent” yeast. The virtues of these compounds are that they preferred sources of energy for bacteria that produce volatile fatty acids (Hong K H et al 2016). Th was confirmed by research in Laos and Vietnam, which has shown that feeing cattle with the by-product of farm-based rice wine production (Sangkhom et al 2017) led to increases in the concentration of proportion acid in the rumen VFA. Similar responses to feeding yeast-fermented rice to cattle were reported by Nguyen et al (2023) and in goats by Nguyen thi Thu Hong et al 2023). As the formation of propionate results in an increase in the demand for hydrogen, it competes with the needs of methanogens that require hydrogen for the reduction of carbon dioxide to methane.
It follows from the above discussion that the objective of the fermentation is to release polysaccharides (eg: beta-glucan) from the cell wall of the yeast.
Beta-glucan and related polysaccharides are soluble in water, thus a simple test for water-soluble dry matter in the end-product of the fermentation could be a simple test of the degree to which beta-glucan has been made available as an energy source for bacteria that produce VFA. The close relationship between the percentage of yeast that is used in the fermentation and the percentage of water-soluble dry matter after the fermenting is completed is a simple test of the “potency” of the YFR as a supplement to increase the production of propionic acid in the rumen fermentation (Figure 2).
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| Figure 2. Effect of percentage of yeast add
to the YFR on the content of water-soluble DM at the end of the fermentation (Nguyen T T H 2022 personal communication) |
The in vitrorumen incubation system has played an important role in developing the concept of “yeast-fermented rice” (YFR) as a supplement to reduce the production of methane in the rumen fermentation (Preston et al 2019). The first experiments used polished rice as the fermentation medium (Sangkhom et al 2019). However, to avoid competition with the human diet, the polish rice has been replaced by broken rice which is one of the by-products from the milling process that remove the husk and most of the protein and oil. Broken rice is usually sold as livestock feed.
It is important to stress that the objective of the fermentation is not to promote growth of the yeast but to use its capacity firstly to convert soluble carbohydrates to ethanol and, when these are exhausted, the yeast enters a process of auto-hydrolysis of the yeast cell wall which results in the release of polysaccharides such as “Beta-glucan”. The negative effect from “feeding” the yeast was shown in an experiment where urea and di-ammonium phosphate were combined with the yeast during the fermentation (Sangkhom et al 2019). The result was an increase in production of methane instead of the planned decease (Figure 3).
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| Figure 3. Adding urea and DAP to the fermentation increased the production of methane (Sangkhom et al 2019) |
Poly-saccharides are only produced when polish rice or broken rice is the fermentation medium. Both of these products have had the major part of the protein removed in the processing of the grain in the rice mill.
When the remaining traces of nutrients are exhausted, the yeast begins to convert soluble carbohydrate in the rice into ethanol. Finally, when all the available substrate has been utilised, the yeast enters a process of auto-hydrolysis in which polysaccharide compounds such as Beta-glucan are released from the cell wall of the yeast. These compounds are water soluble and have the unique properties of being preferred sources of energy for bacteria that produce volatile fatty acids especially propionic as is shown by the direct relationship between the level of YFR and the molar property of propionate in the rumen VFA (Figure 4).
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| Figure 4. The curvilinear relationship between proportion acid in the rumen YFR and the concentration of YFR in the fermentation medium. (Nguyen et al 2022) |
Figure 5. Effect of level of YFR on live weight gain of cattle (Nguyen et al 2022) |
As shown in Figure 4, the relationship between propionic acid and the concentration of YFR in the fermentation medium is not linear as the proportion of propionic acid in the rumen VFA reached a peak value when the concentration of YFR was between 3 and 4% of the fermentation medium.
The response curves for animal performance criteria mirrowed that for propionic acid with it peak values corresponding to YFR values between 3 and 4% (Figures 5-7).
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| Figure 6. Effect of level of YFR on feed conversion of cattle (Nguyen et al 2022) | Figure 7. Effect of level of YFR on the methane: carbon dioxide ratio in the expired breath of cattle (Nguyen et al 2022) |
In other words, feeding of YFR levels beyond 4% of diet dry matter appear to cause a negative response with poorer growth rate and feed conversion in cattle and specifically led to an increasing the production of methane (Figure 6).
In parallel with this research on cattle, studies were also carried out with growing goats fed a basil diet of ad libitum sweet cassava foliage supplemented with Brewers grains (Sina V et al 2017).
There was a dramatic effect on growth rate with a100% increase when the fresh cassava foliage what supplemented with 4% of Brewers grains (Figure 8).
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| Figure 8. Effect of Brewers grains on the
growth of goats fed ad libitum sweet cassava foliage (Sina V 2017) |
However, in a subsequent experiment in which the level of Brewer's grains was increased to 8% of the diet DM, the response was quite different with a negative trend when levels of Brewers grains exceed 4% of the diet DM (Figure 9). The response was curvilinear with a negative response with levels of brewer’s grans beyond 4% with an increase in the production of methane (Figure 10.)
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| Figure 9.
Effect of the level of supplementary Brewers grains on the
nitrogen retention of goats fed cassava foliage (Thuy et al 2018) | Figure 10. Effect of the
level of supplementary Brewers grains on the ration of
methane:carbon dioxide in the expired gas of goats fed cassava foliage (Thuy et al 2018) |
In a similar experiment with growing cattle in Laos, in which the basal diet of cassava pulp/urea was supplemented with increasing proportions of Brewers grains replacing cassava foliage (Figure 11). There was negative response in growth rate with a major increase in methane production when Brewers grains exceed 5% of the duet DM (Figure 12).
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| Figure 11. There was a curvilinear
relationship between live weight gain and the proportion of Brewers grains in the diet of growing cattle (Keopaseuth et al 2017) | Figure 12. The proportion
of methane in the expired gas from cattle was increased as cassava foliating was replaced by Brewers grains (Keopaseuth et al 2017) |
There were major differences in the content of beta glucan in the Brewers grains compared with the yeast fermented rice (Figure 13).
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| Figure 13. Brewers’ grains contain 40% of
Beta-glucan – twice what is in yeast-fermented rice (Binh P L T personal communication) |
It was therefore to be expected that the level of poly-saccharides reaching the rumen would be more than twice the levels derived from feeding yeast fermented rice. reaching levels which according to the experience with used for making rice would lead to negative responses in both love weight gain and emissions of metering.
We hypothesise that levels of beta glue can and related poly- saccharides in the Brewers grains could be the reason for the reduction in live weight gain and the major increase in methane emission in both goats and cattle when Brewers grains were fed at levels exceeding 4% of the diet DM (Figures 10 and 12).
The conclusion from these experiments is that the beneficial effects of the yeast-fermented rice are achieve with low levels (3 to 4% of the diet DM) and that increasing the level beyond 4% has a negative effect on growth rate and at the same time increases emissions of methane.
The hypothesis to explain these contrasting results, according to the level of YFR (or Brewers’grains) in the diet, is that at high levels of supplementations of YFR, or of Brewers grains, there is an increase in the production of an intermediary compound which has negative consequences on the rumen fermentation and specifically on the production of propionic acid. It is suggested that the metabolite in question may be lactic acid, which has negative effects on fees intake when fed to cattle (South Africa reference). Supporting evidence for this pathway is the report (Viniegras G 2023, personal communication), that the commercial production of lactic acid is by fermentation of the poly-saccharides present in “pulque”, the soluble fraction in the leaves of the Agave plant (Agave spp). We stress that we have no direct evidence that a high levels of supplementations with YFR, and or of Brewers grains results in accumulation of lactic acid in the rumen with negative effects nutrient supply to the host animal and which is reflected in reduced growth rates and increased emissions of methane. We hope to provide evidence for this hypothesis in experiments in progress.
We discuss recent results on the feeding of yeast fermented rice (YFR) to ruminants as a means to modify the rumen VFA and specifically to increase the proportion of propionic acid. The outcome of these changes is an increase in the productivity all the ruminant animal with decreased emissions of methane.
We find that the level of the YFR is critical in order to optimise the effect of the supplement on the rumen fermentation. The results indicate that the level of YFR should not exceed 4% of the diet dry matter in order to optimise the effect of the supplementation on the rumen fermentation, and specifically the proportion of propionic acid in the rumen VFA. When higher levels of YFR (or Brewers| grains are fed this will result in reduced proportions of propionic acid in the rumen VFA and increased emissions of methane.
We suggest this could be the result of an increased supply of poly saccharides leads to the accumulation of lactic acid in the rumen. Support for this idea is the established industrial technology for producing lactic acid using the sap from the sisal plant Agave spp which is rich in polysaccharides.
Most of the research discussed in this paper was supported by the MEKARN III project financed by the Swedish International Development Authority (SIDA).
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Viniegras G 2023 personal communication