METHANE EMISSIONS MEASURED DIRECTLY FROM GRAZING LIVESTOCK IN NEW-ZEALAND

We report measurements of methane emissions from individual ruminant l ivestock-both sheep and dairy cows-grazing pasture typical of New Zeal and lowlands in the temperate southwest Pacific. These are the first m easurements reported from grazing sheep, and among the first from graz ing cattle. The measurement technique, developed at Washington State U niversity, enables emission rates to be determined from analyses of '' breath'' samples collected while grazing. More than 250 measurements o f daily methane emission from 50 sheep (8 months old) were made, with flock-mean emission 18.9 +/- 0.8 ghd(-1) d(-1). Although emissions wer e weakly correlated with feed intake, they represented a 4.6 +/- 0.1% average loss of gross dietary energy. The corresponding mean emission based on 40 measurements of daily emissions from 10 lactating dairy co ws was 263 +/- 10 g hd(-1) d(-1), approximately 6.2% of estimated gros s energy intake. A notable feature was the large inter-sheep variabili ty in daily methane emission (factor of 1.4 range) that could not be a ttributed to variable intake. This would appear to suggest an apprecia ble diversity of methanogenetic response to digestion, and may be sign ificant in the search for strategies to control emissions of this gree nhouse gas. (C) 1997 Published by Elsevier Science Ltd.