Sire by Herd Environment Interaction for Milk Production

Abstract

The importance of interaction between estimates of breeding values of dairy sires and ten contrasting herd environments in which their daughters made records was investigated by estimating variance components for interaction between sires and herd management factors and by correlating sire proofs in contrasting herd environments. Artificial insemination sires were evaluated by a within-season and environmental category contemporary comparison, adjusted for the number of daughters and contemporaries involved. Each environmental factor was studied independently, and the sire proofs constituted observations. Herd environment and season effects were assumed to be fixed, while sire effects were assumed to be random. No interactions of practical importance between sire proofs and herd environments were found when herds were grouped in categories with respect to the extent of use of artificial insemination sires, price received for milk, source of water on pasture, forage feeding methods in winter and in summer, amount of exercise received by cows in winter, and herd size. Results of interaction of sire proofs with grain-feeding levels in winter, and with housing systems were inconclusive. A highly significant interaction involving sire proofs and level of grain feeding in summer was found. The interaction component of variance accounted for 17% of the total variance in sire proofs. Genetic correlations between proofs of the same sires based on their daughters in herds with different levels of grain feeding in summer ranged from 0.54 to 0.79.