Genetic Correlations Between Fleece Shedding and Production Traits Indicate Minimal Trade-Offs When Breeding for Maternal Shedding Sheep.

Abstract

Fleece shedding is becoming an increasingly important trait in sheep production systems focused on meat and dairy, where wool has limited economic value and reducing shearing costs is desirable. For inclusion in breeding programmes, a trait must exhibit genetic variation, sufficient heritability, and have well-defined relationships with other economically important traits, as well as economic or desired value. The aim of this study was to estimate the genetic and phenotypic correlations between fleece shedding, recorded in both lambs and adult ewes, and key production traits currently included in the Australian national genetic evaluation for maternal sheep. Using these relationships, the implications of incorporating fleece shedding into a within-flock maternal sheep breeding objective were also examined through desired gains indexes. Genetic correlations between shedding and body weight, carcase, and most visual traits were generally low, indicating limited biological constraints to simultaneous improvement. In contrast, favourable genetic relationships were observed between shedding and parasite resistance, fleece traits such as greasy fleece weight, fibre diameter, and staple strength. Reproductive traits were associated with weak but significant antagonistic genetic correlations with shedding, with phenotypic correlations also indicating that highly productive ewes tended to shed less. Under the base index (regular index with no emphasis on shedding), genetic progress in shedding was minimal, indicating that explicit inclusion of direct emphasis on shedding is required to achieve meaningful improvement. Within-flock selection index simulations demonstrated that low to moderate (desired improvement of 0.33 to 0.66 of a shedding score in 10 years) inclusion of shedding could be achieved with minimal impact on gains in production traits over a 10-year horizon. However, higher levels of emphasis (> 1 shedding score improvement) on shedding resulted in reduced responses in reproductive traits and increased mature weight, alongside diminishing economic returns. These results demonstrate that fleece shedding can be incorporated into multi-trait breeding programmes with limited trade-offs at moderate levels of selection pressure. However, higher levels of emphasis introduced important biological and economic trade-offs. The findings highlight the importance of balanced breeding objectives to ensure that improvements in fleece shedding do not compromise overall productivity.