Genetic Relationships between Indicator Traits for Fly Strike Resistance and Production Traits in Merino Sheep

Abstract

Fly strike in sheep has been estimated to cost the Australian sheep industry approximately $280m dollars annually (Sackett et al. 2006) as a result of sheep losses, cost of treatment and loss of wool and carcase production and value. Historically Australian sheep producers have surgically removed skin from around the tail (mulesing) to help avoid fly strike. Although this has proved highly successful in the past, increasing public concern for animal welfare has forced sheep breeders to search for alternatives. One such alternative is to breed fly strike resistant sheep that do not require mulesing. While the breeding objective is to reduce fly strike, the trait itself if not conducive to measurement and direct selection. Research has revealed a number of indicator traits that are more readily measured and related to fly strike (James 2008; Greeff and Karlson 2009; Smith et al. 2009). These traits include wool cover, skin wrinkle, scouring (dags), wool colour and fleece rot. There is now a large data set of these traits in the Sheep Genetic database from both industry and research flocks. A subset of these traits is included in routine analyses to estimate Australian Sheep Breeding Values (ASBVs). Accurate estimates of the relationships of these traits with key production traits are required to evaluate the impact of including fly strike in the overall breeding objective and using these traits as selection criteria. Due to the diverse nature of the Australian sheep flock and breeding philosophies and the increased use of across flock sires it is possible that the relationships observed across the entire population may be quite different to those within individual flocks. The aims of this study were firstly, to estimate the genetic correlations between the visual traits and production traits within the Sheep Genetics database, and secondly, to attempt to separate within and across flock genetic relationships.