Does intra-ruminal recycling of fermentation products increase methane production?

Volatile fatty acids (VFA), microbial N, CO₂, CH₄ and microbial polymers are the major products of fermentation of organic matter (OM) in the rumen. Production of CH₄ by ruminants is often predicted using empirical equations (e.g., Blaxter and Clapperton, 1965) or from stoichiometric principles, rather than measured, because of the resources required. For example, if rumen digestible OM intake and VFA production rates are known, the production of microbial fermentation products in the rumen can be predicted (Murray et al., 1978; Nolan, 1999).