The Potential Value of Genetic Differences in Liveweight Loss during Summer and Autumn in Merinos Ewes Differs with Production Environment

Genotypes that lose less weight during summer and autumn when feed quantity and quality is limiting could potentially be grazed at higher stocking rates and therefore increase farm profitability. To determine the potential value of breeding for reduced liveweight loss during summer and autumn whole farm systems modelling was used to predict potential changes to farm profitability for different sheep production systems in south-west Victoria. Based on the assumptions used, genotypes that lost less liveweight over summer and autumn were more profitable in all of the production systems and pasture system scenarios examined. The improvements in profitability were greater for lamb than wool production systems and for systems based on moderate rather than high performance pasture. The analysis also indicated that the potential value of reduced liveweight loss during summer and autumn depended on whether it was assumed that this was achieved through increased capacity to consume low quality feed or through a lower energy requirement for maintenance. More needs to be known about the potential size of the genetic difference in liveweight loss over summer and autumn between animals and to understand the biological mechanisms responsible for these differences to better define the value of this trait to the whole farm.