Genetic parameters for reproductive traits of Holstein cattle in California and Minnesota

Genetic parameters for five reproductive traits were estimated using data f rom 51,528 Holstein cows that were inseminated from April to September 1998 in 1717 herds in California and Minnesota. Nonreturn rate and veterinary-c onfirmed pregnancy rate at 60 and 90 d after insemination were evaluated us ing linear and threshold models, including an additive genetic effect for t he cow being inseminated and a random environmental effect for the service bull. Interval from calving to first insemination was evaluated using a lin ear model, including an additive genetic effect for the cow being inseminat ed. Linear model heritability estimates for 60-d (90-d) nonreturn rate were 1.4% (1.5%) in California and 4.1% (2.7%) in Minnesota. Corresponding esti mates for 60-d (90-d) confirmed pregnancy rate were 1.4% (2.3%) in Californ ia and 1.0% (2.0%) in Minnesota; the proportion of cows with veterinary dat a available 60 d after breeding was 86% in California and 55% in Minnesota. Threshold model heritability estimates were slightly higher than linear mo del estimates in California but were lower in Minnesota, presumably because 25% of the herd-season classes in Minnesota contained either all successes or all failures. Linear model repeatability estimates for the service bull effect on 60-d (90-d) nonreturn rate were 0.5% (0.4%) in California and 0. 3% (0.3%) in Minnesota. Corresponding estimates for 60-d (90;a)confirmed pr egnancy rates were 0.6% (0.2%); in California and 0.1% (0.4%) in Minnesota. Threshold model estimates were slightly higher than linear model estimates in both states. Heritability estimates for the interval from calving to fi rst insemination were 5.8% in California and 6.1% in Minnesota. Despite the low parameter estimates, variation was present among animals, and it shoul d be possible to identify sires that possess superior or inferior reproduct ive characteristics.