The aim of this paper is to review the role of methane in the global warming scenario and
to examine the contribution to atmospheric methane made by enteric fermentation, mainly by ruminants. Agricultural emissions of methane in the EU-15 have recently been estimated at 10.2 million
tonnes per year and represent the greatest source. Of these, approximately two-thirds come from
enteric fermentation and one-third from livestock manure. Fermentation of feeds in the rumen is the
largest source of methane from enteric fermentation and this paper considers in detail the reasons for,
and the consequences of, the fact that the molar percentage of the different volatile fatty acids produced during fermentation influences the production of methane in the rumen. Acetate and butyrate
promote methane production while propionate formation can be considered as a competitive pathway
for hydrogen use in the rumen. The many alternative approaches to reducing methane are considered,
both in terms of reduction per animal and reduction per unit of animal product. It was concluded
that the most promising areas for future research for reducing methanogenesis are the development
of new products/delivery systems for anti-methanogenic compounds or alternative electron acceptors
in the rumen and reduction in protozoal numbers in the rumen. It is also stressed that the reason
ruminants are so important to mankind is that much of the world’s biomass is rich in fibre. They
can convert this into high quality protein sources (i.e. meat and milk) for human consumption and this
will need to be balanced against the concomitant production of methane