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The Effect of Sterile Copulation on Time of Ovulation in Dairy Heifers¹

ABSTRACT

The effect of sterile copulation on the time of ovulation was observed on 25 heifers representing four dairy breeds.

The heifers ovulated, on an average, at 7.7 hr. following the end of estrus when serviced by a vasectomizéd bull, as compared to 9.9 hr. when not serviced. The difference was highly significant.

The average length of non-serviced estrual periods was 21.1 hr., compared with 18.2 hr. for estrual periods during which copulation occurred. Statistical analysis showed the difference to be insignificant.

Sterile copulation had no effect on the length of the subsequent estrual cycle.

¹ Published with the approval of the director of the Wisconsin Agricultural Experiment Station. This study was made possible by a grant from Badger Breeders Cooperative, Shawano, Wisconsin.

² Present address: Cornell University, Ithaca, N. Y.