Abstract
To test the hypothesis that sheep live weight (LW) could be used to improve enteric methane (CH4) 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 CH4 emissions in chambers were measured. The linear functional relationship between DMI and CH4 emissions was positive (r = 0.77) with little breed effect. The relationships between LW and DMI, and LW and CH4 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 CH4 emissions from mature ewes.
Highlights
The agricultural livestock industry is tasked with reducing its contribution to global environmental problems[1]
Intakes were relatively high when offered ryegrass, at over 1 kg DM d−1 for all breed types (Table 2). On this forage type a breed effect of dry matter intake (DMI) remained once the results were expressed on a metabolic live weight (LW) (MLW) basis, with the intakes recorded for the Welsh Mountain and Scottish Blackface ewes being the highest and lowest respectively
Apparent DM digestibility was higher for the forage consumed by the Scottish Blackface ewes, and digestible DMI (DDMI) was similar for all breed types when expressed on a MLW basis
Summary
The agricultural livestock industry is tasked with reducing its contribution to global environmental problems[1]. Equivalent global estimates of annual enteric CH4 emissions from sheep computed at Tier 1 following the Intergovernmental Panel on Climate Change (IPCC) 2006 Guidelines for National Greenhouse Gas [GHG] Inventories[4] were 6,305 kilotonnes, or 132,409 kilotonnes CO2e3. Tier 1 is the most simplified approach to accounting that relies on default emission factors (EFs)[4], and takes no account of variables such as diet type, feed intake, animal breed and body size. In this study the relationship between body size and CH4 emissions was defined, with mature ewes of differing modern sheep breeds being offered herbage cut from low, medium and high digestibility grass-dominated swards. If such a relationship existed it could be used to refine future EFs for sheep for Tier 2 inventory reporting mechanisms in the UK and other temperate countries with pasture-based sheep production systems
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