Do we need to include genetic groups to improve the precision of Merino sire evaluation

The influence of genetic differences among Merino ram sources on sire evaluation was examined by estimating sire X dam flock interactions and including varying numbers of genetic groups to account for ram source differences. It was concluded that across-flock sire evaluation results will be biased (in some cases severely), if no account is taken of ram source through including genetic group in the model. Sire X dam source interactions were relatively small but indicated some heterosis between bloodline crosses that may also need to be included in evaluation models.