| Summary: | The heritability for uniformity of body weight is low, indicating that also accuracy of estimated breeding values (EBV) can be low. The use of genomic information could be one way to increase the accuracy and, hence, obtain higher response to selection. Genomic information can be merged with pedigree information to construct a combined relationship matrix (H matrix) for a single-step genomic evaluation (ssGBLUP), allowing realized relationships of the genotyped animals to be exploited, in addition to the numerator pedigree relationships for ngenotyped animals (A matrix). We compared the predictive ability of EBV for uniformity of body weight in Atlantic salmon, when implementing either A or H matrix in the genetic evaluation. We used double hierarchical generalized linear models based on an animal model (animal DHGLM) for both body weight and its uniformity. With the animal DHGLM, the use of H instead of A significantly increased the correlation between the predicted EBV and adjusted phenotypes, which is a measure of predictive ability, for both body weight and its uniformity (41.1 to 78.1%). When log-transformed body weights were used to account for a scale effect, the use of H instead of A produced a small and non-significant increase (1.3 to 13.9%) in predictive ability. The use of H significantly increased the predictive ability of EBV for uniformity when using the animal DHGLM for untransformed body weight. When using logtransformed body weights, the increase in predictive ability was only minor likely due to the lower heritability foruniformity of transformed body weight, a lower genetic correlation between transformed body weights and their uniformities. In conclusion, the use of ssGBLUP increases the accuracy of breeding values for uniformity of harvestweight and therefore is expected to increase response to selection in uniformity.
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