Practical Approaches to Mitigate Methane Gas Emissions from Ruminants

Practical Approaches to Mitigate Methane Gas Emissions from Ruminants

Dr. Aayush Yadav

Ph.D. (Livestock Production and Management)

Veterinary Assistant Surgeon, Livestock Development Department, Mahasamund-493445, Chhattisgarh, India

Author’s Mail Id: aayush.aayush091@gmail.com

Ruminants produce considerable amounts of methane per unit of feed consumed as part of their normal digestive process. Ruminants like, cattle, buffalo, sheep, goats, deer and camels have rumen (fore-stomach) that contains microbes called methanogens, which are capable of digesting coarse plant material and which produce methane as a by-product of digestion (enteric fermentation). This methane is released in the atmosphere either by the belching or by exhaling or excreta of the animals. The enteric fermentation is one of the biggest anthropogenic sources of methane, a potent greenhouse gas which contributes significantly to the global warming.

Today, Ruminants are seen as culprits of climate change as they are responsible for 14.5% emissions of greenhouse gases globally, with cattle responsible for about 61% of these emissions while pig and poultry each contribute

less than 10% (Anonymous, 2022). Of total greenhouse gases, carbon dioxide shares 76% whereas methane, nitrous oxide, and fluorinated gases shares 16, 6, and 2%, respectively (IPCC, 2014). The most important greenhouse gases are methane and nitrous oxide. Methane has 28 times higher global warming potential whereas nitrous oxide has 265 times higher global warming potential than carbon dioxide. Global warming potential of any gas is measured through the carbon dioxide equivalent (EPA, 2021).

Among the ruminants, cattle emit more methane followed by buffaloes, sheep and goat. The estimated enteric methane emission of cattle was 150.7 g/animal/day, buffalo 137.0 g/animal/day, sheep 21.9 g/animal/day, and goat 13.7 g/animal/day

(Sejian et al., 2011). Without any uncertainty, it is clear that large-scale cattle rearing are a significant driver of the changing climate.  As our appetite for milk and meat increases on a global scale, every day both the number of ruminants and the urgency with which we must combat global warming are rising. Scientists are therefore exploring numerous practical approaches to substantially reduce the methane emissions of our ruminants (Lambrechts, 2021).

1. Rumen Manipulation (Anonymous, 2022)
2. Reducing the methanogens in the digestive system of the ruminant is clearly of interest as this would not only alleviate the methane gas emissions, but also increase the productivity of the cow by saving 6-12% of the energy in the feed which is lost by methanogenesis. However, this is not always a preferred method because the microbial community of the rumen is highly complex i.e. rumen includes hundreds of different species of microbes. Removing one group of microbes affects others and can negatively impact the whole digestive process.
3. Defaunation, the removal of rumen protozoa suggests reduction in methanogenesis as 37% of rumen methanogens are endosymbionts with protozoans. These protozoa-associated methanogens (PAM) are the most active communities in the rumen methanogenesis (Belanche et al., 2014). The protozoa engulf and digest bacteria and cause protein turnover in the rumen. Defaunation increase the microbial protein supply to the host by up to 30% and lead to an increase in growth, milk, or wool production and reduction in methane production by up to 11% (Newbold et al., 2015).
4. The chemical inhibitors of the methanogens like ethylene, chloroform, chloral hydrate and bromoethanesulphonate can reduce methanogenesis. Ethylene was found to inhibit methane formation by 50% at 0.07% ethylene concentration (Liu et al., 2011).
5. Fodders and plants like lucerne, oat, berseem, soybean, Moringa oleifera, contain saponins which act as natural antiprotozoal agents and eliminate protozoa without hampering the bacterial activity.
6. Immunization of ruminants against methanogens to reduce the production of methane is also in practice. However, the results are not very evident as vaccines work particularly on certain microbe strains and there is variation in the efficiency.
7. Another group of rumen microbes, the acetogenic bacteria, has high affinity for the hydrogen ions to produce acetate. But, the affinity of methanogens for hydrogen ions is highest as compared to acetogens to produce methane. So, an exogenous inoculation of acetogens in the rumen to increase their population could develop a competitive environment for the methanogens, thus generating a chance to limit the methane production.
8. Besides, rumen bacteria produce antimicrobial peptides ‘bacteriocins’ that can kill or inhibit the closely related or unrelated bacteria. Bacteriocins also have the tendency to inhibit the methane production. This was confirmed by Lee et al. (2002) where bacteriocin from Streptococcus bovis HC5 (bovicin HC5) inhibited methane production by 50%. Likewise, Santoso et al. (2004) and Callaway et al. (1997) tested the effect of Lactococcus lactis bacteriocin ‘nisin’ on rumen fermentation and observed a 10-36% decrease in methane gas emissions.
9. Nutritional Interventions (Anonymous, 2022; Curnow, 2022; Jones, 2014)
   1. Probiotics reduce methanogens and methane production, while increase the proportion of microbes producing more volatile fatty acids that are used as a source of energy by the ruminants.
   2. Ionophore antibiotics like monensin and salinomycin, organic acids like malate, fumarate or acrylate, and plant secondary compounds such as tannins, saponins or essential oils reduce methanogenesis. Ionophores change the bacterial population from gram-positive to gram negative organisms with a simultaneous change in the fermentation from acetate to propionate. This leads to reduction in hydrogenions required for methanogenesis. Propionates provide energy to the ruminants and improve their performances. Propionate enhancers like calcium propionate also reduce the methane production.
   3. Oils such as linseed, sunflower, coconut, garlic and cotton are effective in methane mitigation.
   4. Fat addition in the diet of ruminant’s aid in methane mitigation. Unsaturated fat will remove hydrogen away from methane production to saturate the fat. Both fats and oils have shown methane emission reductions of 15–20%.
   5. Feed additives like Nitrates, 3-nitrooxypropanol, or Bromochloromethane have also proved to be effective in reducing methane emissions. Adding nitrates to the diet at a specified rate optimises rumen fermentation, and changes the pathway of hydrogen to produce ammonia rather than methane. Nitrate salt licks are available for livestock and can be a substitute to urea. Besides, 3-nitrooxypropanol shows a 20-30% reduction in methane gas emissions in dairy cattle, however, the effect is temporary, which means once the feed additive is removed the emissions will rise again.
   6. Cows fed on maize silage emit less methane than cows fed on grass silage. Ensiled forages tend to lower the methanogenesis.
   7. Do not include grasses in the diet. Grasses contains a lot of fibres which produce more hydrogen when broken resulting in increase in methanogenesis.
   8. Include ground legume forages in the diet of animals for reduction in methane production preferably due to the presence of condensed tannins and low fibre content, high dry matter intake, and faster rate of passage from the GIT.
   9. Grinding and pelleting of forages increases passage rate and reduces methane emitted by the animal.
   10. Accessibility of good quality roughage and urea mineral molasses block to ruminants tends to reduce the methanogenesis.
   11. The more concentrates the ruminant feeds on, the lower the production of methane. High levels of concentrate feeds in diets increase the propionate production, which decreases hydrogen availability for methane Feeding corn to the cattle reduces methane emissions by 7 to 10%. However, concentrate feeding above requirements is undesirable and may lead to acidic environment in the rumen.
   12. Inclusion of structural carbohydrates in the diet reduces methane production, as for methanogenesis, the main substrate is fibrous carbohydrates.
   13. Addition of seaweed (red algae) to ruminant diet at 3% produced 80% reduction in methane emissions from cattle.
10. Management Interventions (Lambrechts, 2021)
    1. Selection of dairy animals of high genetic merit helps in reduction in methane gas emissions. A 1% reduction in methane emission per year through selective breeding is possible which can extend up to 20%.
    2. Another approach could be a decrease in livestock numbers. Fewer the livestock, lesser the methane production. But, this is quite impossible as the demand for milk and meat is continuously rising. This can however be accepted if the per-animal productivity is increased with improvement in reproductive performances so that the number of lower productive animals and replacement heifers can be decreased.
    3. A biological filter, which is in its initial phase of development, can be used for

removing methane from the air in the sheds using methane-eating bacteria. These bacteria convert methane into a kind of bacterial protein which could possibly be used as a fertilizer. The filter assembly has to be almost as big as the shed since the air volume in the shed is large. Further, to capture methane gas the animals have to be kept in the shed which is against animal welfare.
	Fig: Biofiltration of methane from ruminants gas effluent (Ganendra et al., 2015)

1. Adopt rotational grazing as a method to stop continuous usage of the same land for long time, and integrated farming system to help carbon sequestration and reduce methane gas emissions.
2. The livestock slurry (dung + urine + bedding materials + water) should be removed more often from the sheds and disposed properly in covered areas as open slurry would come in contact with the aerobic environment and produce methane. The emission of methane gas is related to the storage time of slurry. The slurry which is removed from the livestock shed daily shows a 75% reduction in methane emissions compared to where the slurry is only emptied every fourth month (Sommer et al., 2009).

References

https://www.pashudhanpraharee.com/carbon-footprint-of-dairy-farming/

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