Two hour chamber measurement provides a useful estimate of daily methane production in sheep

In Australia and New Zealand, the significance of enteric methane (CH₄) production is greater than in many industrialised countries, due to large livestock numbers (AGO, 2005). Consequently, there is considerable interest in both countries in breeding livestock which produce relatively less CH₄ per unit of production, as a mitigation strategy. A necessary step in achieving this aim is acquiring the capacity to quickly and reliably estimate the daily methane production (DMP) of ruminants. Mechanistic models used to predict CH₄ production from animals (e.g. Blaxter and Clapperton, 1965) do not reflect differences that have been observed in individual animals on similar intakes (Goopy et al., 2006); 24 h calorimetry remains the only proven method for discerning these observed differences. Unfortunately, this is difficult, resource intensive, and impractical for screening large numbers of animals. Thus, there is considerable impetus to develop alternative methods which will facilitate estimation of OMP in large numbers of animals. This study assessed six (direct and derived) estimates of enteric methane production against 22 h open circuit calorimetry measurements (CHB₂₂) to determine if a reliable, but less demanding estimate of DMP could be found.