Potential effects of animal management and genetic improvement on enteric methane emissions, emissions intensity and productivity of sheep enterprises at Cowra, Australia

Abstract

The efficacy of technologies to reduce enteric CH₄ emissions from ruminants are typically evaluated on individual animals with little consideration of enterprise scale impacts. While impacts of the many rumen manipulations being studied are hard to anticipate, there is adequate information to assess impacts of farm management changes and potential animal genetic changes on whole farm productivity and enteric CH₄ emissions. Seven common sheep production systems grazing an annual pasture in central New South Wales, Australia, were modelled using GrassGro® (version 3.1.2). A range of animal management and animal genetic strategies were examined for their impact on total enteric emissions, emission intensity (i.e., kg CO₂ equivalent/kg live weight (LW) of animal sold) and profit. Within enterprises, mitigation options were compared at their respective sustainable economic optimum stocking rate as it was assumed that farmers would seek to achieve the highest sustainable profit achievable from a finite land resource. Management options considered were choice of lambing time, mating ewes for the first time as lambs rather than yearlings, and feeding lambs to reduce time to slaughter. The potential for using selective animal breeding was also tested, with sheep physiological parameters being altered in GrassGro® to represent genetic improvement in fecundity, LW gain, residual feed intake and CH₄ yield. In general, the management choices delivering lowest emission intensity were also the most profitable within sustainability constraints. Mating maiden ewes as lambs was only effective in reducing enterprise emissions intensity in self-replacing flocks (i.e., no purchased replacements). When stocking rates were at the sustainable economic optimum, choice of enterprise or management had little influence on total enteric emissions from the enterprise. If decisions are guided solely by economics, farmers are likely to continue with similar levels of production (and emissions) until a price on enteric CH₄ emissions makes the sheep enterprise unprofitable, or an alternative more profitable enterprise than sheep grazing emerges. Improving animal genetics for residual feed intake or CH₄ yield offers opportunity to reduce enterprise emissions, but industry progress toward higher genetic merit for these traits is expected to be slow due to relatively low heritability and competing economic imperatives for progress in other traits.