Effects of Bull Exposure on Post-partum Interval and Reproductive Performance in Beef Cows

Spring calving beef cows were utilized to study the effect of bull exposure early postpartum on return to estrus and fertility. In the spring of 1985 and 1986, cows were randomly exposed to epididectomized bulls 3 to 7 days after calving until beginning of the breeding season or not exposed to bulls. Cows were observed for estrus twice daily beginning approximately 4 weeks after the start of calving until synchronization. I n 1986, blood samples were collected weekly by jugular venipuncture during heat detection and serum progesterone concentrations were determined. ALL cows were synchronized with Synchro-Mate B and inseminated 48 hours after implant removal. Calves were removed for 48 hours following implant removal. Each year a group of cows was selected from the two treatment groups and cannulated at estrus following Synchro-Mate B implant removal. Blood samples were collected at 15-minute intervals for 2 hours and every 2 hours for 46 hours for determination of luteinizing hormone concentration. Bull exposed cows had a shorter (Pa.09) interval to first estrus in 1985 and there was no difference (P\u3e.05) in 1986. The percentage exhibiting estrus prior to synchronization was greater (P\u3e.01) for bull exposed than nonexposed in 1985 and there was no difference (P\u3e.05) in 1986. There was no difference (P\u3e.05) in conception rates to the timed insemination in 1985 and 1986 and the total percentage pregnant did not differ (P\u3e.05) in either year. Bull exposure may reduce the interval from calving to first estrus and increase the percentage cycling prior to breeding, but conception rates are not influenced

Effects of Bull Exposure on Postpartum Intervals and Reproductive Performance in Beef Cows: A progress Report

The effects of bull exposure on time from calving until estrus, conception rates and calving interval were studied for mature beef cows. In the spring of I985 and 1986, cows were randomly allotted to one of two treatment groups. Cows were exposed to vasectomized bulls after calving until breeding or no bull exposure. Cows were heat detected twice daily and blood samples were collected weekly to determine progesterone levels. Heat detection data and progesterone levels indicated onset of estrous cycles occurred earlier in bull exposed cows than non-exposed cows. Conception rates to a timed insemination were not different between the two groups. Bull exposed cows tended t o calve earlier