Trans-Tasman genetic evaluations of sheep

Abstract

Until recently it was not possible to compare the genetic merit of sheep between Australia and New Zealand in a technically valid manner. However some breeds now have sufficient sires with progeny in both countries to allow robust genetic evaluations based on performance and pedigree information from both countries. Corriedale and Coopworth breeders in the two countries have conducted across-flock, across-country evaluations using the Sheep Improvement Ltd (SIL) and Sheep Genetics (SG) genetic evaluation systems. Compared to within country evaluations, breeding values (BVs) from the across-flock evaluation were very similar (r=0.96-1.00) when the same system (SIL or SG) was used to estimate BVs. BVs generated from the combined data set by the two systems had lower but still strong correlations(r=0.69-0.89) for most traits. This variation was attributed to different analysis models, including genetic parameters, and performance being measured at somewhat different ages. Ultrasound scan traits were least well correlated (r=0.14-0.65), most likely due to SIL producing BVs adjusted to constant age while SG produces BVs adjusted to constant carcass weight. It was concluded that the best option for genetic evaluation of combined datasets from the two countries is to exchange and combine data but to conduct genetic evaluations and produce reports within-country.