Estimate of methane production from rumen fermentation

A method for the assessment of CH4 emission from dairy cows, based on in vitro volatile fatty acids (VFA) production, is described. 15 energy rich feedstuffs, 12 protein feedstuffs and 15 forages were in vitro fermented using rumen fluid as inoculum. Methane production for each feedstuff was calculated from net concentration of volatile fatty acids after 24 hours of fermentation according to the following stoechiometry: Glucose + 2 H2O → 2 acetate + 2 CO2 + 4 H2; Glucose + 2 H2 → 2 propionate + 2 H2O ; Glucose → 1 butyrate + 2 CO2 + 2 H2; CO2 + 4 H2 → CH4 + 2 H2O and taking in account the `dilution rate' of feedstuffs, estimated according to the Cornell University model. These data were used to estimate the CH4 production in cows (live weight 650 kg, annual milk production:7550 kg, fat content 3.8%). Calculated annual methane emissions based on in vitro trials were: 182.74 kg CH4 /cow or 137.05 kg C–CH4 /cow (diet with corn silage); 182.56 kg CH4 /cow or 136.92 kg C–CH4/cow (diet without corn silage). If compared with estimastes obtained from IPPC (1996) detailed methodology, the above estimates is 35% higher. A critical evaluation of reliability of in vitro data is given.