Reducing Methane Emissions from Ruminant Animals

Abstract

Mathison, G.W., Okine, E.K., McAllister, T.A., Dong, Y., Galbraith, J. and Dmytruk, O.I.N. 1998. Reducing methane emissions from ruminant animals. J. Appl. Anim. Res., 14:1–28. In 1992 it was estimated that 30 x 1012 g more methane was emitted into the atmosphere than was removed, with animals being considered the largest single anthropogenic source. Ruminants produce 97% of the methane generated in enteric fermentation by animals. Estimates for methane emissions from animal wastes vary between 6 and 31% of that produced directly by the animal with the most likely value being between 5 and 10% globally. Although methanogenic bacteria can improve the efficiency of fermentation preventing the accumulation of reducing ruminal hydrogen, alternative means of channeling hydrogen and electrons are possible. Methane inhibitors can reduce methane emissions to zero in the short term but due to microbial adaptation the effects of these compounds are quickly neutralized and feed intake is often depressed. Methane emissions can be reduced by about 18% through the use of ionophores in the short term but there are indications that methanogens as well as other members of the microbial population can adapt to their presence. Defaunation reduces methane production by 20 to 50% depending upon diet. Although methane production can be reduced by including unsaturated fatty acids in the diet, the metabolizable energy content of the diet may not be improved by such additions. Methane emissions per unit of feed consumed from sheep and cattle fed hay diets appear to be quite similar but differences between other ruminants have been measured The most practical way of influencing methane emissions per unit product is to increase productivity level since the proportion of feed energy required to just maintain the animal will be reduced, methane production falls with increased intake level, and the animal may go to market sooner. The most promising avenues for future research for reducing methanogenesis are the development of new products for reducing protozoal numbers in the rumen and the use of bacterocins or other compounds which specifically target methanogenic bacteria.