Ruminants and environment: methanogenesis.

Methane, the most important greenhouse gas after carbon dioxyde, contribute s for 16% to the greenhouse effect. Only 30% of total methane emission orig inates from natural sources, whereas 70% is linked to human activities, inc luding livestock production. Rumen methanogenesis can be incorporated into models of different levels of complexity, based on stoichiometry and kineti cs of fermentation and estimation of energy content of nutrients. Neverthel ess, recent efforts in estimating ruminant methanogenesis remain subject to important variability, both on the animal and population level. In general , methane production in the digestive tract of production animals is estima ted to be responsible for 22% of the anthropogenic sources. Attempts have b een made to decrease this contribution, using methane inhibitors such as lo ng chain fatty acids, halogenated methane analogues, antibiotics and biotec hnological interventions such as defaunation or reductive acetogenesis. How ever, none of the proposed methods for methane inhibition is acceptable nor applicable today due to the interaction of inhibitors with different ratio ns or individual animal characteristics and series of interrelated effects associated with consumer scepticism towards certain additives.