Conception rates of Holstein bulls for artificial insemination on a California dairy.

Data of milk production and reproduction were collected from a 2,500-cow dairy in California for measuring conception rates of bulls for artificial insemination. The bulls were placed into groups of low, medium, or high conception rates. Mean conception rates were 38.2%, 55.7%, and 66.1%, range 34% to 70%. To predict the conception-rate group of a bull required 30 services. There were no differences in average number of lactations and days to first service of the cows bred to the three groups of bulls. Cows bred to the bulls with high conception rate produced 667 kg more milk than cows bred to bulls with low conception rate. Cows bred to the low bulls were bred, on the average, in mid-July, whereas cows bred to the other two groups were bred in June and May. The cost to this dairy for using low conception rate bulls was $21,000.