Effect of Estrus-AI interval on timed AI pregnancy rates in beef cows

We hypothesize that insemination with fresh extended semen will improve the AI pregnancy rate due to its prolonged longevity in female reproductive tract compared to frozen thawed semen. The objective of this trial was to determine the effect of fresh and frozen semen on fixed-time AI pregnancy rate in beef cows synchronized with progesterone based CO-Synch protocols and inseminated at different estrus-AI intervals. Angus cross beef cows (N=180) were synchronized with CO-Synch-CIDR protocols for a fixed-time AI. A subset of cows (N=110) received Heatwatch estrus detection system's pressure sensor at CIDR removal to determine the time of estrus. Cows were divided into two groups, inseminated either at 47h (early) or at 67h (late) from CIDR removal with fresh extended (3 million sperm) or of frozen thawed (20 million sperm) semen. Results indicated that cows inseminated at 67 h had numerically higher fixed time AI pregnancy compared to cows inseminated at 47 h [44.4% (40/90) vs. 33.3% (30/90); P=0.13]. Cows inseminated with frozen thawed semen had similar fixed time AI pregnancy compared to fresh extended semen [40.8 (31/76) vs. 37.5% (39/104); P=0.66]. AI-estrus interval was divided into three groups < 0 h (AI occurred before estrus), 0 to 16 h and > 16 h (AI occurred 16 h after estrus). The AI pregnancy rates for fresh semen for the 3 estrus-AI intervals were similar to frozen semen. In conclusion, the fresh semen yielded similar AI pregnancy as frozen semen when inseminated at different estrus-AI interval in a fixed time AI breeding program in beef cows.