Strategies for Reducing Methane Emission from Ruminant Animals
Methane (CH₄) emissions from ruminant animals, particularly cattle, contribute significantly to greenhouse gas concentrations in the atmosphere. As concerns about climate change escalate, there is a growing need to develop and implement strategies that mitigate methane emissions while ensuring the sustainability of livestock production. This essay explores various innovative approaches and management practices that aim to reduce methane emissions from ruminant animals.
Greenhouse gases such as CO2, CH4, NO2 and O3 contribute to climate change and global warming through their absorption of infrared radiation in the atmosphere. Among these gases CO2, contributes 76.7 % while CH4 14.3 % respectively to the total GHG gases. Methane is especially potent traces gas due to its global warming potential, 25 times that of carbon dioxide, and its 12-year atmospheric lifetime; it is the second largest anthropogenic greenhouse gas, behind carbon dioxide. Globally, livestock produces about 80 million tonnes of enteric CH4 annually which is about 18% of total methane emissions (Moss et al. 2000; IPCC 2007). The CH4 produced in a cattle production system will mostly be by enteric fermentation (85–90%) and the rest is produced by the manure. Methane is produced in the rumen as a product of normal fermentation of feedstuffs. Although methane production can also occur in the lower gastrointestinal tract, as in non-ruminants, 89% of methane emitted from ruminants is produced in the rumen and exhaled through the mouth and nose remaining 11% through the anus (Murray et al., 1976). The rising concentration of CH4 is strongly correlated with increasing populations, and currently about 70% of its production arises from anthropogenic sources. Its concentration has more than doubled during 1750 to 2013 (CDIAC, 2013). Methane represents a significant energy loss to the animal ranging from 2% to 12%. Methanogens living on and within rumen ciliate protozoa may be responsible for up to 37% of the rumen CH4 emission. It avoids hydrogen accumulation, which would lead to inhibition of dehydrogenase activity involved in the oxidation. India emerged as the largest contributor to the livestock methane budget, simply because of its enormous livestock population, although the emission rate per animal in the country was much lower than in the developed countries. In Indian conditions the animals are mostly fed on poor quality roughages of low digestibility and emit less methane than exotic cattle of developed countries fed with highly digestible good quality feed.
Mechanism of Methane formation:
CH4 is produced by two types of methanogens, the slow-growing methanogens 130 h produces CH4 from acetate (e.g. Methanosarcina) and fast growing methanogens (generation time 4– 12 h) that reduce CO2 with H2. Acetate and butyrate production results in a net release of hydrogen while the propionate formation is a competitive pathway for hydrogen use in the rumen. Abatement strategies are often limited by the diet fed, the management conditions, physiological state and use of the animal, as well as government regulations; resulting in difficulties applying a one size fits all approach to the problem of enteric methane mitigation.
Methane Reduction Strategies:
Methane mitigation is effective in one of two ways: either a direct effect on the methanogens or an indirect effect caused by the impact of the strategy on substrate availability for methanogenesis, usually through an effect on the other microbes of the rumen. The metabolic pathways involved in hydrogen production and utilization, as well as the methanogenic community are important factors that should be considered when developing strategies to control CH4, emissions by ruminants.
Any given strategy has to address one or more of the following goals: · a reduction of hydrogen production that should be achieved without impairing feed digestion; · a stimulation of hydrogen utilisation towards pathways producing alternative end products beneficial for the animal; and/or · an inhibition of the methanogenic archaea (numbers and/or activity). This should ideally be done with a concomitant stimulation of pathways that consume hydrogen in order to avoid an increase in the hydrogen partial pressure in the rumen and its negative effect on fermentation as described above.
Dietary Composition
Type of Carbohydrates
Increasing the concentrate in the diet of animals reduced methane by 15–32% depending on the ratio of concentrate in diet. Relationship between concentrate proportion in the diet and CH4, production is curvilinear. Replacing structural Carbohydrates from forages in the diet with Non-structural carbohydrates shift of VFA production from acetate towards propionate occurs with the development of starch-fermenting microbes. The low ruminal pH might also inhibit the growth and/or activity of methanogens and of cellulolytic bacteria.The nature and rate of fermentation of carbohydrates influence the proportion of individual VFA formed and thus the amount of CH4, produced. Fermentation of cell wall carbohydrates produces more CH4, than fermentation of soluble sugars, which produce more CH4, than fermentation of starch therefore diets rich in starch that favor propionate production will decrease CH4, production per unit of fermentable organic matter in the rumen. Conversely, a roughage based diet will favor acetate production and increase CH4, production per unit of fermentable organic matter.
Level of Intake:
An increase in feeding level induces lower CH4, losses as % of gross energy intake (GEI). The CH4, loss as % of GEI declined by 1.6 percentage units for each multiple increase of intake. This is caused mainly by the rapid passage of feed out of the rumen and as a result of the increased passage rate; the extent of microbial access to organic matter is decreased, which in turn reduces the extent and rate of ruminal dietary fermentation. About 28% of the variation in CH4, production was attributed to the mean retention time. Also, a rapid passage rate favors propionate production, which is a competitive pathway for the use of H2.
Forage Species and Maturity: Digestion of cell wall fibres increases methane production, by increasing the amount of acetate produced in relation to propionate. Dietary manipulation through increased green fodder decreased methane production by nearly 5-6%. CH4, production in ruminants tends to increase with maturity of forage fed, and CH4, yield from the ruminal fermentation of legume forages is generally lower than the yield from grass forages.
Feeding Frequency:
Low meal frequencies are tending to increased propionate production; reduce acetic acid production and lower CH4, production in dairy cows. This effect is associated with the lowering of methanogens as a result of high fluctuations in ruminal pH, since low meal frequencies increase diurnal fluctuations in ruminal pH that can be inhibitory to methanogens. On the other hand, more frequent feeding was shown to increase the acetate: propionate ratio which is beneficial for methane production.
Forage Preservation:
There is limited information with regard to the effects of forage preservation on CH4, production. Methane production (% of GEI) was shown to be lower when forages were ensiled than when dried. This is because digestion is reduced in the rumen with ensiled forages due to the extensive fermentation that occurs during silage making. Methanogenesis tends to be lower when forages are ensiled than when they are dried, and when they are finely ground or pelleted than when coarsely chopped. The treatment to the roughages will definitely increases digestibility and hence the fermentation reduces due to the passage of the digesta along retention time in the rumen.
Grazing Management: Implementing proper grazing management practices to improve the quality of pastures will increase animal productivity and lower CH4, per unit of product.
Manipulation of Rumen Fermentation
Addition of Fats or Lipids:
Increased lipid content in the feed is thought to decrease methanogenesis. This is due to inhibition of protozoa, increased production of propionic acid, biohydrogenation of unsaturated fatty acid. Unsaturated fatty acids – used as hydrogen acceptors as an alternative to the reduction of carbon dioxide. Fats are added to dairy cattle diets to increase the energy density of diets, enhance milk yield and modify the fatty acid composition of milk fat. It has been shown that the medium chain fatty acids (C8–C16) cause the greatest reduction in CH4, production. So therefore addition of this fatty acid essentially lowered down the emission of methane from the ruminants.
Ionophores: Ionophores are highly lipophilic substances, which are able to shield and delocalize the charge of ions and facilitate their movement across membranes. Monensin is the most commonly used and studied ionophore, with others such as lasalocid, tetronasin, lysocellin, narasin, salinomycin and laidomycin also being used commercially. Ionophores, which are added to ruminant diets to improve the efficiency of feed utilization, have been shown to decrease CH4, production.
Defaunation: Defaunation, which is the elimination of protozoa from the rumen by dietary or chemical agents, has been shown to reduce ruminal CH4, production by about 20 to 50% depending on the diet composition. Protozoa in the rumen are associated with a high proportion of H2 production, and are closely associated with methanogens by providing a habitat for up to 20% of rumen methanogens. Removal of protozoa (defaunation) from the rumen is often associated with an increased microbial protein supply and improvement of animal productivity. Hence, defaunation has been suggested as a way to reduce CH4, production with little or minimal effect on rumen digestion. The reduced ruminal methanogenesis observed with defaunation can be attributed to factors such as a shift of digestion from the rumen to the hind gut or the loss of methanogens associated with protozoa during defaunation.
NEW POTENTIAL MITIGATION OPTIONS
Probiotics: There is very little information on the effects of probiotics on CH4, production in dairy cattle. The effects of the most widely used microbial feed additives, Saccharomyces cerevisiae and Aspergillus oryzae, on rumen fermentation were earlier studied in vitro. Aspergillus oryzae was shown to reduce CH4, by 50% as a result of a reduction in the protozoal population. It has been shown that yeast culture influenced microbial metabolism and improved DMI, fiber digestion, and milk production in lactating cattle. However, the specific mode of action is still unknown. It has been proposed that probiotics provide nutrients, including metabolic intermediates and vitamins that stimulate the growth of ruminal bacteria, resulting in increased bacterial Bacteriocins: Direct suppression of methanogens may be possible through stimulation of natural or introduced ruminal organisms to produce bacteriocins as a means of biological control. Bacteriocins are bactericidal compounds that are peptide or protein in nature, and are produced by bacteria. However, little information is available concerning their effect on methanogenesis. They often display a high degree of target organism specificity, although many have a very wide spectrum of activity. Nisin, an exogenous bacteriocin produced by Lactococcus lactis, is the best studied and understood bacteriocin.
Archaeal Viruses:
Another possible method of biological control of methanogens is the use of archaeal viruses (bacteriophages). Bacteriophages are obligate pathogens that can infect and lyse bacteria and methanogens. They are highly host-specific. Although the presence of bacteriophages in the rumen is well known knowledge of archaeal viruses is still limited.
Immunization: In the past 3 year, researchers in Australia have vaccinated sheep with a number of experimental vaccine preparations against methanogens, so that the animals produce antibodies to methanogens. Methane production was reduced between 11 and 23% in vaccinated animals and productivity was improved. No long- or short-term adverse effects on sheep were found. Researchers anticipate that commercial vaccines will allow a 3% gain in animal productivity and a 20% reduction in CH4, production. It is important to note that the vaccines currently under development are based on cultivable methanogens. Plant extracts (condensed tannins, saponins, essential oils): There is growing interest in the use of plant secondary compounds as a CH4, mitigation strategy. For tannin-containing plants, the antimethanogenic activity has been attributed mainly to the group of condensed tannins. Hydrolysable tannins, although they also affect methanogens, are usually considered more toxic to the animal and have not been extensively tested. Two modes of action of tannins on methanogenesis have been proposed in vitro by a direct effect on ruminal methanogens and an indirect effect on hydrogen production due to lower feed degradation. However, the antiprotozoal effect of saponins may be transient and is not always accompanied by a decrease in CH4, production indicating that other modes of actions are also important. Similar to tannins, the source of saponins is important. Many biologically active molecules present in essential oils have antimicrobial properties that are capable to affect rumen fermentations. Among them, it has recently been shown that garlic oil and some of its components decreased CH4, production. This was attributed to the toxicity of organosulphur compounds such as diallyl sulphide and allicin on methanogens. This effect was corroborated for allicin by quantitative PCR (McAllister and Newbold, 2008).
Number and productivity of animals:
Livestock reduction through culling is also decrease the load of methane producing unproductive animal which leads to decrease the emission of methane. Proper livestock management especially in developing countries such as reducing the incidence of disease and reproductive problems can decrease CH4 emission in a herd for each unit of production.
Variations in total GHG emission: Change in production system From a forage-based to a concentratebased system and low-producing animals to high-producing animals results in simultaneous variation of all GHG. Winter feeding system based on concentrates with high-yielding cows produced 37% less enteric CH4, compared to grass system with low-producing cows, but this difference was compensated by a much higher CH4 emission from slurry, compared to the very low emission from urine and faeces on pasture. Grass-based system in New Zealand has a lower global warming potential than in European more intensive systems.
Manure management: it refers to capture, storage, treatment, and utilization of animal manure in an environmentally sustainable manner. The sharply different manure management practices in India, as compared to the western countries, lead to much lower methane emissions from manure. (a) Better manure management and methane recovery techniques. The flaring process decreases up to 95% of harmful atmospheric effect of methane. (b) To create a condition unfavourable for methane generation.
Time budget for reducing methane through various strategies:
Timeline for development –Mitigation practice for the dairy industry– Expected reduction in methane
Immediate –Feeding oils and oilseeds 5 – 20%
Higher grain diets 5 – 10%
Using legumes rather than grasses 5 – 15%
Using corn silage or small grain silage rather than grass silage or grass hay 5 – 10%
Ionophores 5 – 10%
Herd management to reduce animal numbers 5 – 20%
Best management practices that increase milk production per cow 5 – 20%
5 years —-Rumen modifiers (yeast, enzymes, directly fed microbials) 5 – 15%
Plant extracts (tannins, saponins, oils) 5 – 20%
Animal selection for increased feed conversion efficiency 10 – 20%
10 years-— Vaccines 10 – 20%
Strategies that alter rumen microbial populations 30 – 60%
Understanding Methane Production in Ruminants
- Rumen Microbial Activity
Methane is produced in the rumen during the microbial fermentation of ingested feed. Certain microbes, known as methanogens, play a key role in this process as they produce methane as a byproduct of their metabolic activity.
- Enteric Fermentation
Enteric fermentation, the digestive process occurring in the stomach compartments of ruminants, is the primary source of methane emissions in these animals. Strategies targeting this specific aspect of digestion can effectively reduce methane production.
Innovative Strategies for Methane Mitigation
- Methane Inhibitors and Modifiers
- Feed Additives:
- Tannins: Compounds found in some forages and tree leaves, tannins have been shown to reduce methane emissions by inhibiting methanogen activity.
- Seaweed Additives: Certain seaweeds, such as Asparagopsis, contain compounds that can significantly reduce methane production when included in the diet.
Chemical Inhibitors:
- Nitrate Supplementation: Nitrate can serve as an alternative hydrogen sink in the rumen, inhibiting methanogenesis and reducing methane emissions.
Nutritional Management
High-Quality Forages:
- Providing ruminants with high-quality forages that are easily digestible can improve feed efficiency and reduce the overall methane emissions per unit of feed consumed.
- Grain Supplementation:
- Including grains in the diet can alter the microbial population in the rumen, leading to a decrease in methane emissions.
Genetic Selection
Breeding for Low-Methane Traits:
- Selective breeding programs can target animals with genetic traits associated with lower methane production. This involves identifying and breeding animals that naturally produce fewer methane emissions.
Improved Animal Husbandry Practices
Grazing Management:
- Implementing rotational grazing practices can improve forage utilization, leading to better digestion and reduced methane emissions.
Optimized Feeding Practices:
- Feeding animals according to their nutritional needs and using precision feeding technologies can reduce the overall methane output per unit of production.
Education and Outreach
Farmer Training:
- Educating farmers about the environmental impact of methane emissions and providing information on sustainable practices encourages the adoption of methane mitigation strategies.
Research and Innovation:
- Supporting research initiatives focused on developing novel methane reduction technologies and practices ensures a continuous stream of innovative solutions.
Challenges and Considerations
- Economic Viability:
- Some methane mitigation strategies may involve additional costs, and it is essential to assess the economic feasibility of implementation for farmers.
- Animal Health and Welfare:
- Changes in diet and management practices must prioritize the health and welfare of the animals. Unintended consequences, such as negative impacts on nutrient absorption or animal behavior, need to be carefully considered.
- Global Adoption:
- Achieving meaningful reductions in methane emissions requires widespread adoption of mitigation strategies globally. International collaboration and policy support are crucial for successful implementation.
Conclusion
Reducing methane emissions from ruminant animals is a multifaceted challenge that demands a comprehensive and collaborative approach. Innovative strategies, ranging from feed additives and genetic selection to improved nutritional management and educational outreach, offer promising avenues for mitigating methane emissions while maintaining sustainable livestock production. As the global community intensifies its efforts to address climate change, the implementation of these strategies, coupled with ongoing research and technological advancements, can contribute significantly to the reduction of methane emissions from ruminant animals. In doing so, we can foster a more environmentally responsible and resilient future for the livestock industry.
There are a number of nutritional technologies for improvement in rumen efficiency like, diet manipulation, direct inhibitors, feed additives, propionate enhancers, methane oxidisers, probiotics, plant secondary metabolites and defaunation. Keep in mind to reduced methane from ruminants we can have best option such as genetic selection for low residual feed, animal population and their productivity. Change in production system from forage based to concentrate based help to reduced methane emission from livestock along with efficient utilisation and disposal of manure definitely reduced methane from ruminants.
Compiled & Shared by- This paper is a compilation of groupwork provided by the
Team, LITD (Livestock Institute of Training & Development)
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Reference-On Request.
