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Effects on Reproductive Performance of Administration of GnRH to Early Postpartum Dairy Cows^1,2,

Colorado State University, Fort Collins 80523

Abstract

Three-hundred and thirty-five lactating dairy cows from two herds were used to compare the effects on reproductive performance of intramuscular injections of 100 µg gonadotropinreleasing hormone (GnRH), 250 µg GnRH or saline given on day 13, 14 or 15 postpartum. The incidence of ovarian cysts or uterine infections was not reduced after GnRH injection. Culling rate for infertility did not differ in either herd between GnRH- and saline-treated control cows. In the herd in which breeding began earlier in the postpartum period (Herd B), injection of 250 µg GnRH resulted in a better (P<.05) calving to conception interval (81 vs 96 days), better first service conception rate (74.5 vs 56.0%), better overall conception rate (70.6 vs 51.1%) and a lower number of services per conception (1.23 vs 1.74) than in the controls. In reproductively well-managed herds, injections of 250 µg GnRH, given to lactating dairy cows 2 weeks after calving, may increase fertility.

¹ Anim. Reprod. Lab.

² The authors achnowledge Dr. R. Ripple, Abbott Laboratories, North Chicago, 1L, for providing GnRH.