cows, bull exposure, GnRH, postpartum interval, fertility
Spring calving beef cows were utilized in a study to determine the effects of bull exposure (BE) and Gonadotropin Releasing Hormone (GnRH) administration on return to estrus and reproductive efficiency. Cows were either exposed to an epididectomized bull soon after calving until the breeding season or not exposed to bulls (NE). All cows were synchronized with Synchro-Mate B (SMB). One-half of the BE and NE cows were implanted with GnRH at SMB implant removal in 1987 or given an injection of GnRH at breeding in 1988. Each year, 20 cows were bled hourly for 80 consecutive hours after SMB removal. There was no difference (P>.05) in days from calving to first estrus, calving date, number of cows cycling before breeding or conception rate to the synchronized estrus between BE or NE cow groups. In 1987 GnRH implants reduced (P<.05) the time from SMB removal to the pre-ovulatory LH peak by 23.5 hours. However, there was no difference (P>.05) in LH peak levels, duration of Luteinizing Hormone (LH) peak or conception rate. Bull exposure and GnRH implants had little effect on the interval from calving to first estrus or reproductive performance.
Number of Pages
South Dakota State University
Copyright © 1988 South Dakota State University
Miller, H.L. and Haigh, R.H., "Effects of Bull Exposure and Gonadotropin Releasing Hormone on Postpartum Interval and Fertility in Beef Cowsa" (1988). South Dakota Beef Report, 1988. 16.