Genetic relationships of breech cover, wrinkle and wool coverage scores with key production traits in Australian Merino sheep

Merino breeding programs seeking a genetic solution to reduce the incidence of flystrike require estimates of genetic correlations between both flystrike itself and its indicator traits with wool production and quality traits that affect the profitability of a Merino enterprise. This will enable Merino producers to predict the outcome of selection strategies and genetic improvement programs that include reducing flystrike on flock productivity and profitability. Genetic correlations of breech cover, wrinkle (breech, body and neck) and wool coverage with liveweight, wool production, wool quality and visual wool traits were estimated from a Merino genetic resource flock. Breech cover had favourable genetic correlations with liveweight that increased in magnitude with age at scoring (−0.34 to −0.66). However, the magnitude and direction of the genetic correlations of breech cover traits with wool production traits differed with the age of assessment and were mostly negligible. The genetic correlations between breech cover and the measured wool quality traits, where significant, tended to increase in magnitude with the age of assessment. Apart from a favourable genetic association with the severity of fleece rot (0.22-0.26) the genetic correlations between breech cover and the visual wool quality scores were all antagonistic. The wrinkle traits (breech, neck and body) each tended to have similar genetic relationships with the key Merino production traits. These were favourable with liveweight (−0.27 to −0.50), antagonistic with wool production, fibre diameter and most visual wool quality scores but favourable with staple length, fibre diameter variability and midbreaks. Wool coverage however, had few significant genetic relationships with key production traits and these were highly variable between age expressions. These genetic correlations of breech cover and wrinkle scores with key Merino enterprise profitability traits, together with the previously published phenotypic variances, covariances and phenotypic correlations, can now be used to predict the outcomes of multi-trait breeding programs seeking to reduce the incidence of flystrike with minimal impact on wool production or quality.