Methane production by sheep in relation to temporal changes in grazing behaviour

Domesticated ruminant animals are thought to contribute significantly to th e global annual emission of methane. CH4 emission from sheep was measured u sing a system designed to allow grazing under near-natural conditions in th e southwest of the UK. In two studies with mature ewes (5-year-old) methane emissions were measured continuously for up to 8 days in a large polythene tunnel. Small wind-tunnels were used to draw air through the polythene tun nel and a gas chromatograph was used to measure methane concentrations in a ir entering and in air leaving the tunnel. Air speeds were used to calculat e air volume flow through the tunnel, and temperature and humidity were als o measured. For periods within these two studies, simultaneous recordings w ere made of animal behaviour using an automatic system that measured jaw mo vements; these data provided a continuous record of the time spent by each animal eating, ruminating or idling. Results suggested that the behavioural patterns of sheep within a polytunnel were similar to those found previous ly for sheep at pasture, although the amount of time spent eating in the tu nnel was less. Methane emission rates tended to follow this behavioural pat tern with peak emission rates corresponding to peaks in eating activity. Em ission rates fell when eating gave way to ruminating. Methane emissions ave raged 20.31 per day per animal, a value similar to previous estimates made using the same system, although methane emissions measured by other workers in open circuit respiration chambers are consistently higher. This experim ent helps to explain the animal factors which partly control the contributi on that ruminants make to global methane emissions. (C) 2001 Elsevier Scien ce B.V. All rights reserved.