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Role of Ruminant Animals in Global Climate Change

Ruminant animals are great contributors to the human food chain due to their ability to utilize complex polysaccharides in plant cell walls (cellulose, hemicelluloses and pectin), which are otherwise non digestible to any of the mammalian digestive enzyme and turn these into meat and milk for human consumption. Digestion of these polysaccharides in ruminant diets is attributable to anaerobic biodegradation of these compounds into their respective monomers by microorganisms (bacteria and fungi) present in the forestomach of the animals. In spite of their contribution to the human food chain, ruminant animals are often debated as one of the contributing factors in global climate change due to the emission of CH4 as a byproduct of fermentative digestion of feedstuffs in the forestomach. In addition, production of methane by ruminants causes a significant amount of feed energy loss which could be used for animal growth and production if methane production is prevented.

Domestic ruminant animals are one of the important anthropogenic sources of methane which contribute approximately 23% (81 Tg of CH4) of the total anthropogenic annual methane production, and this is the second largest (fossil fuel is the first) source of anthropogenic methane production. Approximately two thirds of total methane production by domestic ruminants is contributed by cattle and the rest is shared by other domestic ruminants like buffalo, sheep, goats etc. Several factors influence the enteric methane emissions from ruminants. Daily dry matter intake, digestibility of the feed, amount of fibres and soluble carbohydrate in diet, type of volatile fatty acids (VFAs) produced during fermentation (acetate: propionate ratio) etc, effect the amount of enteric methane production. Similarly, animal species, breed and composition of the microbial population in the rumen and rumen pH also affect methane production. 

Thus, reduction in methane emission from ruminants has twofold benefits. Firstly, it will help to reduce the global warming due to greenhouse gases and secondly, it reduces feed energy loss. Reduction in methane emission will result in higher growth and productivity of ruminant and improve the efficiency of feed utilization with the same amount of energy supplied. Reduction in GHG emissions from ruminant animals could be done earlier than from other sectors and requires less effort and financial investment thus making the strategy more feasible.

P.S.: References are available on request.