SIRE BY HERD INTERACTIONS FOR MILK YIELD AND COMPOSITION TRAITS

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Abstract
A total of 13,561 Holstein 305-day lactation records from 779 Quebec and Maritime herds enrolled on the Dairy Herd Analysis Service were used to evaluate the importance of sire × herd interactions for milk yield and composition traits. Sire × herd interaction accounted for 4.1, 1.1, 0.3, 2.6 and 5.6% of the total variation of milk, fat and protein yield and fat and protein percent, respectively. Genetic parameter estimates obtained under two different models, a full model that accounted for sire × herd interaction and a reduced model that ignored it, were examined. Heritabilities of milk, fat and protein yield and fat and protein percent were, respectively: for the full model, 0.36, 0.47, 0.45, 0.59 and 0.31 and for the reduced model, 0.49, 0.50, 0.46, 0.66 and 0.46. Phenotypic correlations between the traits were not appreciably different when estimated under the full and reduced models. Genetic correlations between the yield traits were also similar when estimated under the full and reduced models, but genetic correlations between yield and percentage traits were more stongly positive, or less negative, when sire × herd interaction was accounted for. The genetic correlation between fat and protein percent was larger under the reduced model than under the full model.