Genetic improvement of hill sheep - Impacts on profitability and greenhouse gas emissions

Scottish Blackface hill sheep from two research flocks, based in environments of differing climatic severity, were selected for 8 years based on a selection index incorporating ewe and lamb traits, designed to improve flock sustainability and profitability. Compared to a control line of sheep kept at average performance, after 8 years of selection, sheep selected on this index have shown increased overall profitability, largely due to an increase in the weight of lambs at weaning (2-2.5 kg, depending on farm). A model was used to estimate greenhouse gas (GHG) emission changes in hill sheep systems when performance traits were altered, to investigate the potential to use genetic selection as a tool to reduce GHG. Results from this model suggested that the actual genetic changes observed in the hill flocks are likely to have increased GHG emissions, both at the level of the breeding ewe and per kg of lamb produced, mainly as a result of an increase in ewe mature size (2.8-3 kg difference vs. the control line after 8 years of selection). Any future selection index designed to minimise GHG emissions, would need to incur heavier penalties for increasing ewe mature weight, compared to the current economic index, which would be likely to reduce selection response in lamb growth. These changes are only likely to occur if payment or subsidy systems were to change in a way that would reward producers for reducing GHG emissions.