Genomic estimation of additive and dominance genetic variation and their effect on the accuracy of genomic prediction of sheep

Additive and dominance variance of weaning weight (WWT) and post weaning weight (PWWT) for purebred Merinos and crossbreds of Merino and other breeds were estimated. Additive and dominance genomic relationships were calculated based on 48,599 SNP marker genotypes. Dominance variation was 3.61% and 5.58% of phenotypic variance for WWT and PWWT, respectively in purebreds and 9.2% and 17.1% for WWT and PWWT in crossbreds. The likelihood of the model was improved by including dominance effects, particularly for crossbred data. The accuracy of within breed genomic breeding value based on prediction from purebreds was similar for additive and additive plus dominance model but showed between 0.3% and 2.1% increase based on prediction from crossbreds and using additive plus dominance model. Fitting both additive and dominance effects of marker genotypes provides either similar or higher GBV accuracy depending on the value of dominance variance.