Impact of ewe genotype on sire breeding values in genetic evaluation of Merino body composition and components of reproduction

There are anecdotal concerns among Merino breeders that Australian Sheep Breeding Values (ASBVs) of sires do not always predict performance when sires are used in a different genetic background, or in other words, when joined to different ewe genotypes (often referred to as 'bloodlines'). Whilst previous analyses (Egerton-Warburton et al. 2019) found significant but small sire x ewe genotype interactions for post-weaning and hogget fleece traits in Merino sheep, it might be expected that heterosis is more likely to affect traits associated with fitness. Mortimer and Atkins (1997) found significant direct and maternal heterosis effects on component reproduction traits using data from a large crossing experiment. The extent to which these effects would be influencing Merino reproduction traits assessed in central test sire evaluation and on-farm progeny testing is, however, unknown.