Genetic and genomic strategies to fast-track the improvement of breechstrike resistance in Merino sheep

Dr Sonja Dominik (view profile)

S. Dominik, CSIRO Agriculture and Food, Armidale, NSW
J. Greeff, Department of Primary Industries and Regional Development, Perth, WA
J. Smith CSIRO Agriculture and Food, Armidale NSW

Genetic improvement of breechstrike resistance in Merino sheep provides a permanent solution, adding significantly to the efforts to reduce reliance on mulesing in the Australian Merino sheep industry. On commercial sheep breeding operations, flystrike is prevented through a range of management strategies, including crutching and chemical treatment.

While effective, increased use of chemicals increases the risk of blowflies becoming resistant to the available treatments. The difficulty of genetic improvement strategies for breechstrike resistance is that the direct phenotype is very difficult to record in particular because the level of resistance or susceptibility to flystrike is masked by good husbandry and chemical treatments.

The Breechstrike Resource Flocks in Western Australia and New South Wales, funded through Australian Wool Innovation Ltd, were initiated in 2005 and ran for 10 years.

In 2009 breeding values were established for the key breechstrike indicator traits, such as breech cover, breech wrinkle and dag, and are now available through MERINOSELECT, Australia’s genetic evaluation system for Merino sheep. There are however differences between sheep types, in the breech traits, variability and thus likely rates of genetic gain.

Genomic strategies may be used to fast-track genetic gains in these important but difficult traits by enabling selection on potential candidate genes that are associated with resistance or susceptibility, particularly for the Super Fine Merino type that is higher in wrinkle and has less variation in the trait. A total of 1,524 animals from the Breechstrike Resource flocks have been genotyped.

Genotypes at a density of 700K were obtained on 948 animals and another 576 animals at a genetic marker density of 50K. Here we provide an overview of the genetic and genomic approaches that assists in improving breechstrike resistance in Merino sheep and how they support the efforts to reduce the reliance on mulesing and chemicals to control breech strike