Identifying indicator traits for breech strike in Merino sheep in a Mediterranean environment

Abstract

Data from 2833 unmulesed Merino lambs from 49 sires and 1535 dams that were born from 2005 to 2009, were used to identify indicator traits for breech strike in a Mediterranean environment. Sheep were managed in a normal production environment where no preventative treatments were applied to protect them from being struck by flies, but were immediately treated when found to be fly struck. Seventy-seven skin, body conformation, wool, disease and production traits that may contribute to breech strike and that could qualify as potential indicator traits were recorded on progeny at birth, weaning, post-weaning, yearling, spring and at pre- and post-hogget age at ~18 months of age. In all, 31% of ewes and 22% of rams were fly struck in the breech area between birth and hogget shearing. The heritability of and the phenotypic and genetic correlations between the potential indicator traits and breech strike were estimated. The results showed that breech strike is a heritable trait (h2 = 0.51 ± 0.10), and that the most important indicator traits for breech strike were dags, scored at any time, especially at hogget age (rg = 0.81 ± 0.15), spring (rg = 0.77 ± 0.13) or at weaning (rg = 0.64 ± 0.00), urine stain scored at weaning (rg = 0.54 ± 0.13) and marking (rg = 0.51 ± 0.15), neck wrinkle at hogget age (rg = 0.46 ± 0.13) and breech cover (rg = 0.32 ± 0.15) scored at post-weaning shearing. These traits could be used to select indirectly for breech strike resistance in a Mediterranean environment.