Increasing estradiol benzoate, pretreatment with gonadotropin-releasing hormone, and impediments for successful estradiol-based fixed-time artificial insemination protocols in dairy cattle

Abstract With the objective to optimize fixed-time artificial insemination (FTAI) protocols based on estradiol benzoate (EB) and progesterone (P4), we performed 2 experiments (Exp.) in dairy cows. In Exp. 1 (n=44), we hypothesized that increased EB (EB3=3mg vs. EB2=2mg) on d 0 would improve synchronization of ovarian follicle wave emergence. Likewise, in Exp. 2 (n=82), we hypothesized that a GnRH treatment on d −3 (early in a follicular wave on d 0) versus d −7 (presence of a dominant follicle on d 0) would better synchronize wave emergence. Moreover, results from both experiments were combined to identify reasons for the lack of synchronization. All cows were treated with EB at the time of introduction of a P4 implant (d 0). On d 7, cows were given 25mg of prostaglandin F 2α ; on d 8, the implant was removed and cows were given 1mg of estradiol cypionate. All cows received FTAI on d 10. In both experiments, daily ultrasound evaluations were performed and, in Exp. 2, circulating P4 was evaluated during the protocol. Pregnancy per artificial insemination (P/AI) was determined on d 31 and 59 after FTAI. In Exp. 1, EB dose did not change time to wave emergence, but EB3 compared with EB2 decreased the percentage of cows with a corpus luteum on d 7 (19.8 vs. 55.3%) and time to ovulation (10.4 vs. 10.9 d). In Exp. 2, although we detected a tendency for delayed follicle wave emergence after the start of the FTAI protocol in cows ovulating to GnRH given on d −7, there was no difference in percentage of cows with a synchronized wave emergence (~80%). Regardless of treatment, more cows with P4