REDUCING METHANE EMISSIONS FROM RUMINANT ANIMALS

In 1992 it was estimated that 30 x 10(12) g more methane was emitted i nto the atmosphere than was removed, with animals being considered the largest single anthropogenic source. Ruminants produce 97% of the met hane generated in enteric fermentation by animals. Estimates for metha ne emissions from animal wastes vary between 6 and 31% of that produce d directly by the animal, with the most likely value being between 5 a nd 10% globally. Although methanogenic bacteria can improve the effici ency of fermentation preventing the accumulation of reducing ruminal h ydrogen, alternative means of channelling hydrogen and electrons are p ossible. Methane inhibitors can reduce methane emissions to zero in th e short term but due to microbial adaptation the effects of these comp ounds are quickly neutralized and feed intake is often depressed Metha ne 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 presen ce. Defaunation reduces methane production by 20 to 50% depending upon diet. Although methane production can be reduced by including unsatur ated 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 qui te similar but differences between other ruminants have been measured The most practical way of influencing methane Emissions per unit produ ct is to increase productivity level since the proportion of feed ener gy required to just maintain the animal will be reduced, methane produ ction falls with increased intake level, and the animal may go to mark et sooner. The most promising avenues for future research for reducing methanogenesis are the development of new products for reducing proto zoal numbers in the rumen and the use of bacterocins or other compound s which specifically target methanogenic bacteria.