Ruminants and environment: methanogenesis.

Methane, the most important greenhouse gas after carbon dioxyde, contributes for 16% to the greenhouse effect. Only 30% of total methane emission originates from natural sources, whereas 70% is linked to human activities, including livestock production. Rumen methanogenesis can be incorporated into models of different levels of complexity, based on stoichiometry and kinetics of fermentation and estimation of energy content of nutrients. Nevertheless, 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 estimated to be responsible for 22% of the anthropogenic sources. Attempts have been made to decrease this contribution, using methane inhibitors such as long chain fatty acids, halogenated methane analogues, antibiotics and biotechnological interventions such as defaunation or reductive acetogenesis. However, none of the proposed methods for methane inhibition is acceptable nor applicable today due to the interaction of inhibitors with different rations or individual animal characteristics and series of interrelated effects associated with consumer scepticism towards certain additives.