Methane emissions from grazing sheep and calves

Methane emission from sheep was measured using a system designed to allow grazing under near natural conditions. In four studies, with periods of continuous measurement of between 4 and 10 days and with animals ranging in age from 7 months to 4.5 years, emission of methane averaged 13.3 g day(-1) per animal, equivalent to 4.9 kg year(-1) per animal. Consideration is given to the dry-matter intake of the animals used in these studies and its possible effects on methane production. From the data it is estimated that the total UK sheep population could contribute 247 kt of methane annually to the atmosphere. Diurnal fluctuations in hourly rates of emission were recorded, with methane production increasing during daylight to reach a peak at or near sunset and then declining towards sunrise. This pattern corresponded with diurnal changes in the grazing behaviour of sheep that have been reported elsewhere. In two preliminary studies using calves, methane emissions averaged 74.5 g day(-1) per animal, with some evidence of a diurnal pattern; emissions were close to theoretical predictions based on animal live weight. (C) 1997 Elsevier Science B.V.