Can live weight be used as a proxy for enteric methane emissions from pasture-fed sheep?

Abstract

To test the hypothesis that sheep live weight (LW) could be used to improve enteric methane (CH 4) emission calculations, mature ewes of 4 different breeds representative of the UK sheep industry were studied: Welsh Mountain, Scottish Blackface, Welsh Mule and Texel (n = 8 per breed). The ewes were housed and offered ad libitum access to fresh cut pasture of three different types, varying in digestibility: (a) a relatively high digestibility monoculture of perennial ryegrass (Lolium perenne), (b) a medium digestibility permanent pasture comprising a range of grass species, and (c) a relatively low digestibility native grassland pasture comprising mainly Molinia caerulea. Individual LW, feed dry matter intake (DMI), and CH 4 emissions in chambers were measured. The linear functional relationship between DMI and CH 4 emissions was positive (r = 0.77) with little breed effect. The relationships between LW and DMI, and LW and CH 4 emissions were also positive but weaker, regardless of pasture type. It is concluded that change to LW was a poor indicator of DMI and has limited value in the prediction of enteric CH 4 emissions from mature ewes.