1418
Effect of timing of artificial insemination and estrus expression using sexed semen on pregnancy rates in Holstein dairy cows
The use of sexed semen has become important in dairy herds across the U.S. but reported lower conception rates have limited the adaptation in some herds. The objective of this study was to determine if timing of AI and expression of estrus impacted fixed-time AI pregnancy success with sexed semen. Primiparous and multiparous lactating Holstein cows (n=130) were synchronized with a Presynch-Ovsynch protocol (PGF d -29; PGF d -19; GnRH and CIDR® insertion d ‑9; PGF and CIDR removal d -2; GnRH d 0) starting at 35 DIM. The cows were allotted into a 2x2 factorial randomized block (lactation) design with 1) sexed (n=68) versus conventional (n=62) semen and 2) insemination at second GnRH (n=54) versus 16 h later (n=76). Follicle size was determined in all cows by transrectal ultrasonography at GnRH and ovulation was confirmed on d -5 and 4. Only those cows that ovulated after AI were utilized in the analysis (n = 130). Estrus detection was determined by visual observation with the aid of tail chalk. Blood samples were collected on d -16, -9, -2, 0 and 4 to determine circulating concentrations of progesterone and estradiol by RIA. Data were analyzed using the GLIMMIX procedures of SAS. There was a significant effect of time of insemination (P = 0.04) and estrus expression (P = 0.02) on pregnancy success. Cows inseminated 16 h after GnRH had greater pregnancy success compared to cows bred at time of second GnRH (53% vs 35%, respectively), and cows expressing estrus had greater pregnancy success compared to cows not expressing estrus (54% vs 34%, respectively). However, there was no effect of semen (P = 0.20; 50% vs 38% for conventional and sexed, respectively) or any interaction of semen by estrus (P = 0.55); semen by time (P = 0.47); or time by estrus (P = 0.23) on pregnancy success. There was no difference between treatments (P = 0.62) or between cows that became pregnant and cows that did not (P = 0.45) for follicle size at the second GnRH injection, but cows that expressed estrus had larger (P < 0.01) follicles than cows that did not express estrus. In conclusion, pregnancy success was significantly influenced by time of insemination and estrus expression, but was not influenced by semen, or any interactions.
Keywords: Fixed-time AI, sexed semen, estrus