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 AI bulls. Genetic predictions of merit for calving ease have been available for Holstein AI bulls in the US since 1978. A threshold 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 ease. Pedigree information from sires, sons, and grandsons is also included in the analysis to improve the reliability of genetic predictions for bulls that have pedigree data available. Each sire's genetic prediction for calving ease is reported as the expected percentage of difficult births of primiparous cows. National in scope, genetic predictions for calving ease are used internationally by breeders of dairy cattle to minimize the risk of difficult births of primiparous cows and to increase the use of AI for young cows.