Breeding for resilience and resistance in Merino sheep

Abstract

Resilience is poorly defined in the Australian sheep industry. However, there are a number of traits available to the industry which provide scope to understand an individual's potential resilience and resistance to environmental stressors. These traits include body condition score, body weight and condition change throughout the year and reproduction. The parasite resistance traits of worm egg count and fly strike resistance are also of interest. Currently, genetic improvement programs are focussed on improving the quality and quantity of wool growth, reproduction and lean meat production. However, significant phenotypic and genetic correlations between production and resilience and resistance traits could be leading to unintentional changes in the performance of the national flock when faced with differing environmental and disease challenges. These relationships are not always favourable making it a complex area for breeders to easily resolve, in particular how much emphasis to place on each of these traits. Furthermore, the Australian sheep industry is located across a range of variable environments and thus the importance of these resilience and resistance traits is likely to vary across those environments. We combined the current knowledge of the relationships between traits and evaluated the impact of various measurement and index selection scenarios to compare the impact of both production, resilience and resistance traits on current breeding strategies available to the Merino industry. The results suggest that selection purely on production traits has and may continue to influence the resilience of the Merino component of the national sheep flock. At this point in time breech wrinkle is the only trait that is predicted to change in an undesirable direction when using the standard MERINOSELECT indexes made available by Sheep Genetics. More desirable gains can be achieved in the additional resilience and resistance traits when they are valued in the indexes, with generally little impact on the standard production traits. When more accurate economic values for resilience and resistance traits can be derived, breeding objectives should be revised and appropriate selection traits identified, and accommodated into the selection indices used by breeders.