Assessing genetic variability in flystrike resistance across expression levels in Australian Merino sheep

This work aimed to provide guidance to breeders on the level of flystrike expression required to achieve effective selection and to develop genomic reference data for future prediction. Genetic parameters and breeding values were compared across different expression thresholds (1% to 10%) using data sourced from 21 research and industry breeder flocks. Among the thresholds examined (1% to 10%), a 2.5% threshold was adequate for excluding data with no genetic variation for breech strike while retaining sufficient data for analysis. Previously, a 5% threshold was considered effective for capturing data with adequate variation, primarily from research flocks with minimal flystrike prevention practices. Lowering this threshold to 2.5% enables greater breeder participation by making it more achievable to obtain information for selection purposes. As flystrike resistance has proven to be heritable, breeding for genetic resistance offers a sustainable, long-term solution, helping to reduce flystrike. Additionally, this change supports a broader breeding approach to reduce flystrike, potentially minimising reliance on chemical treatments and management practices.