A Field Study on Fertility and Purity of Sex-Sorted Cattle Sperm

The study assessed the fertility and purity of sexed semen used for inseminating Holstein-Friesian heifers in commercial dairy herds. Sex-sorted semen from 4 proven Holstein-Friesian bulls and available under commercial conditions was used on nulliparous Hol- stein heifers reared on 61 dairy farms of northern Italy. Data from 536 artificial inseminations with pregnancy diagnosis and 258 calvings were analyzed using the logistic regression procedure. The effects of year and season of insemination or calving, age at insemination or calving, heifer inbreeding, and the sperm dose used for insemination on the probability of a positive preg- nancy diagnosis or of the birth of a female calf, respec- tively, were studied. The overall pregnancy rate for sexed semen was 51% and was affected by year of in- semination and bull. Heifers inseminated with sexed semen from 2 bulls had lower pregnancy rates than heifers inseminated with sexed semen from other bulls. Purity of the sexed sperm, based on the proportion of female calves, was 87% and this percentage was not affected by explanatory variables included in the logis- tic regression. The results demonstrate that bulls differ in terms of fertility of their sexed semen. Careful selec- tion of the insemination sires used for sorted semen is advisable for avoiding low fertility inseminations.