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Heritability and Repeatability of Conception Rate of Bulls in Artificial Breeding

New Zealand Dairy Board, Wellington

ABSTRACT

The conception rate for bulls used in artificial breeding is defined as the proportion of cows not returning to first service within 49 days of insemination. Heritability of conception rate is estimated as 0.55 ± 0.26 from 75 sire-son pairs in 3 yr of breeding, the sires averaging 1,792 inseminations and the sons 376. Repeatability is estimated from 314 sires used in 2 yr as 0.69 ± 0.05, based on an average of 1,344 inseminations per sire per year. These estimates are obtained after eliminating from the mean squares the inherent sampling variation that arises from the binomial distribution in estimating the conception rate of a bull. The mathematical method of doing this is presented.