A total of 58 Holstein cows from a commercial dairy herd that had been unable to get pregnant after repeated services were induced into lactation. Cows were assigned to two estrous synchronization protocols: ovsynch (n= 20; GnRH 7 d before and 48 h after PGF2α, with fixed artificial insemination (AI) at 24 h after the second GnRH injection), and heatsynch (n= 38; GnRH + PGF2α 7 d later + estradiol cypionate (ECP) 24 h after PGF2α and AI 48 h after ECP). Pregnancy was diagnosed by palpation at 40 d after AI. All cows in both groups exhibited estrous, but due to the high occurrence of cystic follicles (30 and 13% for ovsynch and heatsynch, respectively), only 13 and 33 cows in the ovsynch and heatsynch group, respectively, were inseminated. Conception rates at 40 d post-insemination did not differ between groups. Cows with intense estrous did not differ between groups. It was concluded that timed artificial insemination in cows induced to lactation and free of cystic follicles produced acceptable conception rates at first AI in those unable to conceive in its previous lactation.
Timed artificial insemination, estradiol cypionate, reproduction, estrous
