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

Genetic parameters for five reproductive traits were estimated using data from 51,528 Holstein cows that were inseminated from April to September 1998 in 1717 herds in California and Minnesota. Nonreturn rate and veterinary-confirmed pregnancy rate at 60 and 90 d after insemination were evaluated using linear and threshold models, including an additive genetic effect for the cow being inseminated and a random environmental effect for the service bull. Interval from calving to first insemination was evaluated using a linear model, including an additive genetic effect for the cow being inseminated. 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 estimates for 60-d (90-d) confirmed pregnancy rate were 1.4% (2.3%) in California and 1.0% (2.0%) in Minnesota; the proportion of cows with veterinary data available 60 d after breeding was 86% in California and 55% in Minnesota. Threshold model heritability estimates were slightly higher than linear model 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-d) confirmed pregnancy 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 first insemination were 5.8% in California and 6.1% in Minnesota. Despite the low parameter estimates, variation was present among animals, and it should be possible to identify sires that possess superior or inferior reproductive characteristics.