Dietary, environmental and microbiological aspects of methane production in ruminants

Methane gas is produced in the rumen by methanogenic bacteria as a metabolic end product. The energy released by bacteria in the process of methane formation can be used for bacterial cell formation. Methane formation acts as an electron sink into which the hydrogen from all ruminal microorganisms drains, allowing a higher yield of adenosine triphosphate. Factors such as the type of carbohydrate in the diet, level of feed intake, digesta passage rate, presence of ionophores or lipids in the diet, and ambient temperature influence the emission of methane from ruminants. Methanobrevibacter spp. appear to be the major methanogens in the rumen, but it is likely that phytogenetic analyses will identify new species. The biochemical reduction of carbon dioxide to methane is well defined, and it has been shown that interspecies hydrogen transfer between methanogens and ruminal bacteria prevents the accumulation of reduced nucleotides and the inhibition of feed digestion. The development of strategies to mitigate methane production in ruminants, without causing a negative impact on ruminant production, continues to be a major challenge for ruminant nutritionists and microbiologists. Enhancement of the reduction of carbon dioxide to acetate and direct genetic manipulation of methanogens are two interventions that may further reduce methane losses of ruminants.