Methane production from commercial dairy rations estimated using an in vitro gas technique

An in vitro gas production technique was used to measure total gas and methane (CH4) production from commercial total mixed rations (TMR) for lactating dairy cows. The TMR were collected from six commercial dairy farms in the San Joaquin Valley of California (USA), and the campus dairy at the University of California in Davis, for evaluation using an in vitro gas production technique to determine the CH4 concentration of total gas. The TMR samples were analyzed for nutritional components and in vitro assays were conducted to measure neutral detergent fibre digestibility, and total gas and CH4 production. The TMR were similar in nutrient composition, with CP ranging from 163 to 185 g/kg DM. There were differences among TMR in total gas production at 6, 24, 30, 48 and 72 h of in vitro incubation, and the TMR differed (P < 0.05) in rate of, and potential, gas production. The proportion of CH4 in total gas did not differ among TMR at 6 and 24 h of incubation, but differences did occur at 48 and 72 h. An average of 33.8 ml CH4/g DM incubated was produced by 24 h of incubation, and approximately 0.80 of total CH4 was produced during the first 24 h of incubation. Estimates of the quantity of CH4 produced from this procedure were similar to those previously reported in vivo, suggesting that it can be used to estimate CH4 production from rations fed to dairy cows. This may make it a suitable tool to evaluate the extent to which CH4 emissions by dairy cattle can be altered, either by changes in rations or by feeding compounds to modify rumen fermentation. (c) 2005 Elsevier B.V. All rights reserved.