GENETIC PREDICTION FOR CALVING EASE IN THE UNITED-STATES - DATA, MODELS, AND USE BY THE DAIRY-INDUSTRY

Dystocia of Holsteins has a major economic impact on the dairy cattle industry. Genetic evaluation of AI sires for calving ease is sponsored by the National Association of Animal Breeders. The AI organizations and dairy records processing centers collect data from herds that have progeny of Al bulls. Genetic predictions of merit for calving ease ha ve been available for Holstein Al bulls in the US since 1978. A thresh old model was implemented during 1988. The threshold model adjusts for the effects of herd-year, season, sex of calf, parity, and birth-year group of sire to predict the genetic merit of each sire for calving e ase. Pedigree information from sires, sons, and grandsons is also incl uded in the analysis to improve the reliability of genetic predictions for bulls that have pedigree data available. Each sire's genetic pred iction for calving ease is reported as the expected percentage of diff icult births of primiparous cows. National in scope, genetic predictio ns for calving ease are used internationally by breeders of dairy catt le to minimize the risk of difficult births of primiparous cows and to increase the use of AI for young cows.