| Livestock Research for Rural Development 33 (5) 2021 | LRRD Search | LRRD Misssion | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
In this review we describe the research which led to: (i) the identification and testing of a fermentation byproduct (Rice wine distillers” byproduct - RDB) with the capacity to reduce methane emissions from ruminants; and (ii) the development of a supplement made by fermenting polished rice (or cassava root) with yeast ( Saccharomyces cerevisiae) which had similar capacity as “: RDB” to reduce methane “in vitro”.We consider that both products can be described as “prebiotics” because they are derived from the yeast cell wall and when fed at low levels (4%) to a ruminant diet they: (i) improve animal health by reducing HCN toxicity from cassava-rich feeds; and (ii) increase the production of propionic acid in the rumen and indirectly improve animal performance as well as reducing missions of methane.
We hypothesize that, tannins present in the leaves of cassava, combine with protein (and other soluble nutrients) making them resistant to fermentation in the rumen. This allows their escape to the intestine where the low pH disrupts the tannin-nutrient bonds and the nutrients become available for enzymic digestion and absorption. At the same time, beta-glucan and related compounds derived from the fermented yeast cell wall selectively provide energy for the growth of bacteria that produce volatile fatty acids in a process whereby they selectively compete for electrons with bacteria that produce methane.
Key words: cassava, HCN, prebiotic, propionic acid, tannin, thiocyanate, toxicity
The idea that generated this research was based on observations during the development of cattle fattening system based on cassava root pulp, urea and cassava foliage (Phanthavong et al 2014, 2016a, b, 2017). It was observed that when the animals were fed foliage from bitter cassava, rich in HCN precursors, they had a craving to eat “brewers’ spent grains” that were being fed to cattle in adjacent pen. It was hypothesized that the brewers’ grains were acting as a “prebiotic” providing habitat enabling the evolution of rumen microbial communities capable of detoxifying the HCN when the cassava foliage was consumed by cattle. To test this hypothesis, ensiled brewers’ grains were supplemented at 5% of the diet of local “Yellow” cattle fed ensiled cassava root and urea and given sweet cassava foliage or fresh, water spinach (Inthapanya et al 2016). The 33% increase in N retention when the cattle were fed the low level of brewers’ grains was considered to be evidence that the brewers’ grains were having a positive “prebiotic” effect on overall animal wellbeing rather than being simply an additional source of “bypass” protein. It was notable that the effect of the brewers’ grains on N retention was more pronounced when cassava foliage was the source of dietary protein rather than water spinach.
The implication of these observations was that the cassava foliage was a superior source of bypass protein (solubility of the protein was 30% for cassava compared with 67% for water spinach) but this potential advantage was constrained by the negative effect of the HCN precursors (which were ameliorated by the addition of 5% of brewers’ grains to the diet).
Further confirmation of the role of brewers’ grains as a potential prebiotic was the research of Binh et al (2017), which showed that cattle had low feed intakes and did not gain weight when their diet contained 30% of bitter cassava foliage (Figure 1). However, as soon as they were given a supplement of brewers” spent grains, their feed intake improved and they began to grow at the same rate as comparable animals fed sweet cassava foliage. Analysis of the urine of these animals showed that there was a direct relationship between the introduction in the diet of brewers’ grains and the excretion in the urine of thiocyanate (Figure 2) - the product of the detoxification of HCN.
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| Figure 1.
Introducing a supplement of brewers’ grains in the diet of cattle fed bitter cassava foliage led to an immediate improvement in growth rate (Binh et al 2017) |
Figure 2. Secretion of thiocyanate in the urine of cattle fed cassava
pulp-urea and BG-RS (brewers’ grains plus rice straw), CFB (bitter cassava foliage), CFB-BG (bitter cassava foliage plus 4% brewers’ grains), CFS: (sweet cassava foliage), or BG-RS (brewers’ grains at 25% of diet DM plus rice straw 1% of diet DM) (Binh et al 2017) |
The follow-on from this research was the appreciation that in SE Asia the family scale production of “rice wine” was a widespread activity. In contrast with “beer” production, rice “wine” involved a further step of “distillation” to raise the “alcohol” content of the “wine”. The final residue (known locally as “Hem” in Vietnam, “Quilao”in Laos and “Bar-Ran” in Cambodia) had a similar composition to Brewers’ grains (about 23% of protein in DM)) which made it an excellent feed supplement for pigs (Manh et al l2009)). However, the low content of solids (23%) precluded its use mainly as a feed for the pigs in the household of the wine.
The value of the “Rice distillers’ byproduct (RDB)” as a locally available alternative to brewers’ grains was evaluated in two “on-farm” experiments in Laos (Figures 3-6). Feed ingredients (Photo 1) for local “Yellow” cattle were ensiled cassava root (with urea added prior to feeding) and, sweet cassava foliage ad with or without RDB at 4% of the diet DM.
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| Photo 1. The tree main ingredient of the diet (ensiled cassava root, rice distillers’ by product (RDB) and sweet cassava foliage) (Sengsouly and Preston 2016) | ||
The effect of the RDB was similar to that observed for brewers’ grains with improvements in live weight gain (Figure 3) and feed conversion (Figure 4), but with the additional benefit of a 20% reduction in enteric methane (Figure 5).
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| Figure 3. Effect of rice distillers’ byproduct on the live weight
gain of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sengouly and Preston 2016) |
Figure 4. Effect of rice distillers’ byproduct on feed conversion of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sengsouly and Preston 2016) |
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Figure 5. Effect of rice distillers’ byproduct on methane:carbon
dioxide ratio in expired brath of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sengouly and Preston 2016) |
The above findings were confirmed in the second feeding trial (Figures 6-8; Sangkhom et a (20 17), with additional data showing a positive effect of the RDB on volatile fatty acid production manifested as a decrease in the acetic: propionic ratio in the rumen VFA (Figure 9).
The results of the on-farm trials thus confirmed the hypothesis that designing ruminant feeding systems to have a low carbon footprint will also result in improved growth rate and feed conversion.
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| Figure 6.
The effect of rice distillers’ byproduct on the live weight gain of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sangkhom et al 2017) |
Figure 7. The effect of rice distillers’ byproduct on feed conversion of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sangkhom et al 2017) |
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| Figure 8.
Effect of rice distillers’ byproduct on the methane:carbon
dioxide ratio in expired breath of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sangkhom et al 2017) |
Figure 9.
Effect of rice distillers’ byproduct on the acetate:propionate ratio in rumen fluid of “Yellow” cattle fed ensiled cassava root, urea and cassava foliage in Lao PDR (Sangkhom et al 2017) |
The logical sequence in this research was to develop a simple method to reproduce the rice distillers’ by-product but without the associated production of rice wine (Sangkhom et al 2019). Sticky and normal rice were steamed (farmer system), or not not steamed, fermented with yeast under anaerobic conditions for 7 days and then boiled or distilled (to simulate the farmer method) or not heated. There were no benefits, as measured by effects of the simulated RDB on methane production, in the in vitro system, from steaming the rice or from boiling or distilling the rice after fermentation.
On the basis of these findings, it was hypothesized that the critical step in the development of the RDB was probably the initial fermentation with the yeast and that the “steaming” and use of “sticky rice” were elements that facilitated the production of rice wine but had no carry-over effect on the RDB in its role as a potential prebiotic.
The next step was to test the effect of adding sources of nutrients (urea and dicalcium phosphate) that would encourage the yeast to “grow” rather than produce alcohol as occurs in the rice wine production. The results were dramatic in that the product of the fermentation of the N and P supplemented yeast did not reduce methane production in the in vitro incubation (Sangkhom et al 2019).
The implication from these results were that the initial fermentation of the rice with yeast “alone” was the critical step in the process, not only for generation of alcohol, but also to transform the residual yeast into the “spent” form characterized by the breakdown of the yeasty cell wall carbohydrates into Oligo or polysaccharides such as beta glucan and manans such as beta-glucan and related strictures.
The following experiment was therefore designed to compare the product from the simple yeast fermentation of polished rice with the classical RDB as the additive in the in vitro rumen simulation of the cattle fattening system based on ensiled cassava root, urea and cassava foliage. Leaves from sweet and bitter cassava varieties were compared as the source of bypass protein to create conditions in which the effect of the fermented rice would be more clearly manifested (Sangkhom et al 2020).
The fermented rice additive reduced methane by 24.3% when the protein source was bitter cassava and by 20.3% when it was sweet cassava. Comparable figures for rice distiller’s byproduct were 20.8 and 15.6 for bitter and sweet cassava (Figure 10).
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| Figure 10.
Effect of rice distillers’ byproduct (RDB) or
yeast-fermented rice on methane production in an in vitro rumen incubation of ensiled cassava root-urea with leaves from sweet and bitter varieties of cassava (Sangkhom et al 2020) |
A recent met meta-analysis (Arndt et al 2021) of 425 publications revealed an average reduction in methane emissions of 21% for five feeding strategies, namely CH4 inhibitors, oils and fats, oilseeds, electron sinks, and tanniferous forages. For the strategies that were more farmer-friendly (grazing grass-legume swards at earlier stages of growth, increasing concentrate: forage ratio and increasing the; level of feeing decreased CH4 emissions by on average 12%.
The research discussed in this paper was supported by the MEKARN III project financed by the Swedish International Development Authority (SIDA).
Arndt Claudia, Hristov W, Price W and 20 more authors 2021 Strategies to Mitigate Enteric Methane Emissions by Ruminants -A Way to Approach the 2.0°C target. agriRxiv DOI. 10.31220/agriRxiv.2021.00040
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.
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. http://www.lrrd.org/lrrd28/2/sang28020.htm
Manh L H, Xuan Dung N N, Kinh L V, Binh T C, Thu Hang B P and Phuoc T v 2009 Composition and nutritive value of rice distillers’ by-product (hem) for small-holder pig production. Livestock Researchfor Rural Development. Volume 21, Article #224. http://www.lrrd.org/lrrd21/12/manh21224.htm
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. http://www.lrrd.org/lrrd26/9/phan26169.htm
Phanthavong V, Khamla S and Preston T R 2016 Fattening cattle in Lao PDR with cassava pulp. Livestock Research for Rural Development. Volume 28, Article #10. http://www.lrrd.org/lrrd28/1/phan28010.html
Phanthavong V, Preston T R, Viengsakoun N and Pattaya N 2016 Brewers' grain and cassava foliage (Manihot esculenta Cranz) as protein sources for local “Yellow” cattle fed cassava pulp-urea as basal diet. Livestock Research for Rural Development. Volume 28, Article #196. http://www.lrrd.org/lrrd28/11/phan28196.html
Phanthavong V, Preston T R and Leng R A 2017 Glycerol supplementation increased growth rates, decreased the acetate: propionate ratio in rumen VFA, and reduced enteric methane emissions, in cattle fattened on cassava pulp-urea, brewers’ grains and rice straw. Livestock Research for Rural Development. Volume 29, Article #36. http://www.lrrd.org/lrrd29/2/phan29036.html
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. http://www.lrrd.org/lrrd28/10/seng28178.html
Sangkhom I, Preston T R, Leng R A, Ngoan L D and Phung L D 2017 Rice distillers’ byproduct improved growth performance and reduced enteric methane from “Yellow” cattle fed a fattening diet based on cassava root and foliage (Manihot esculenta Cranz). Livestock Research for Rural Development. Volume 29, Article #131. http://www.lrrd.org/lrrd29/7/sang29131.html
Sangkhom I, Preston T R, Binh P L T, Phung L D and Ngoan L D 2019 Simulating rice distillers’ by-product with fermented sticky rice; effects on methane production in an in vitro rumen fermentation of ensiled cassava root, cassava foliage and urea. Livestock Research for Rural Development. Volume 31, Article #127. http://www.lrrd.org/lrrd31/8/sang31127.html
Sangkhom I, Preston T R, Ngoan L D and Phung L D 2020 Effect of yeast-fermented rice and rice distillers’ byproduct on methane production in an in vitro rumen incubation of ensiled cassava root, supplemented with urea and leaf meal from sweet or bitter varieties of cassava. Livestock Research for Rural Development. Volume 32, Article #52. http://www.lrrd.org/lrrd32/3/intha32052.html