Yield records of Holstein cows were used to verify the interaction effect on accuracy of sire breeding values. The records of milk yield were adjusted to 305 days of lactation and age of the cow. Variance components for milk yield were estimated using restricted maximum likelihood methodology through two animal models, either not fitting or fitting a sire-by-herd interaction term. Likelihood ratio test was used to verify the effectiveness of including a sire-by-herd interaction effect in the model. Average milk yield was 6,936.13 ± 1,508.36 kg. The variance components estimates were smaller, when the sire-by-herd interaction was fitted, however, residual variance component, were similar for both models. Heritability estimates for milk yield obtained not fitting and fitting the interaction term in the model, were 0.247 ± 0.021 e 0.237 ± 0.021, respectivelly. The proportion of the phenotypic variance due to the sire-by-herd interaction variance, was equal to 0.034±0,005 percent. The logarithm of the likelihood function was highest fitting a sire-by-herd interaction. The breeding values of the sires for 305 day mature milk yield were lower using the model with sire by herd interaction, being of the Spearman correlation value close to unity.
genetic evaluation; milk yield; sire by herd interaction
