Pregnancy rate following artificial insemination or natural service in postpartum estrus synchronized beef cattle

The objective of this study was to investigate the pregnancy rate following artificial insemination (AI) or natural service (NS) in postpartum estrous synchronized beef cattle. A total of 85 Brangus cows, postpartum, were divided into 2 groups. Group 1 consisted of 35 cows and was further subdivided into 7 groups, each consisted of 5 cows that were naturally mated. Group 2 consisted of 40 cows that were artificially inseminated. Estrus synchronization was carried out using a controlled internal drug releasing device (CIDR) containing 1.38 mg of progesterone, for 7 days. Group 1 cows were mixed with bulls at a 1:5 ratio of bull: cows for 7 days and group 2 cows were inseminated 55-58 h aft er the CIDR removal. Pregnancy was determined using transrectal ultrasonography 32 days aft er NS and AI. The pregnancy rate was higher in the NS group (28.6%) than in the AI group (18.0%), but the difference was not significant (P > 0.05).