Measurements of methane emissions from individual sheep and dairy cows grazing typical New Zealand perennial ryegrass/white clover dominant pastures are reported. These are the first measurements reported from grazing sheep, and among the first from grazing cattle. The measurement technique, using a marker gas (sulphur hexafluoride), enables emission rates to be determined from analyses of "breath" samples collected while grazing. More than 250 measurements of daily methane emission from 50 sheep (8 months old) were made, with flock-mean emission 18.9±0.8 g/d. Emissions were weakly correlated with feed intake, and 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 cows was 263±10 g/d, approximately 6.2% of estimated gross energy intake. A notable feature was the large inter-sheep variability in daily methane emission (range 140%) that could not be attributed to variable intake. This would appear to suggest an appreciable diversity of methanogenic response to digestion, and may be significant in the search for strategies to control emissions of this greenhouse gas.
Proceedings of the New Zealand Society of Animal Production, Volume 57, , 130-133, 1997
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