Prostaglandin treatment at the onset of norgestomet and estradiol-based synchronization protocols did not alter the ovarian follicular dynamics or pregnancy per timed artificial insemination in cyclic Bos indicus heifers

The aim of the present study was to evaluate the effects of the PGF2α treatment given at the onset of a synchronization of ovulation protocol using a norgestomet (NORG) ear implant on ovarian follicular dynamics (Experiment 1) and pregnancy per AI (P/AI; Experiment 2) in cyclic (CL present) Bos indicus heifers. In Experiment 1, a total of 46 heifers were presynchronized using two consecutive doses of PGF2α 12 days apart. At first day of the synchronization protocol the heifers received implants containing 3mg of NORG and 2mg of estradiol benzoate (EB). At the same time, heifers were randomly assigned to receive 150mg of d-cloprostenol (n=23; PGF2α) or no additional treatment (n=23; Control). When the ear implants were removed 8 days later, all heifers received a PGF2α treatment and 1mg of EB was given 24h later. The follicular diameter and interval to ovulation were determined by transrectal ultrasonography. No effects of PGF2α treatment on the diameter of the largest follicle present were observed at implant removal (PGF2α=9.8±0.4 vs. Control=10.0±0.3mm; P=0.73) or after 24h (PGF2α=11.1±0.4 vs. Control=11.0±0.4mm; P=0.83). No differences in the time of ovulation after ear implant removal (PGF2α=70.8±1.2 vs. Control=73.3±0.9h; P=0.10) or in the ovulation rate (PGF2α=87.0 vs. Control=82.6%; P=0.64) between treatments were observed. In Experiment 2, 280 cyclic heifers were synchronized using the same experimental design described above (PGF2α; n=143 and Control; n=137), at random day of the estrous cycle. All heifers received 300 IU of equine chorionic gonadotropin (eCG) and 0.5mg of estradiol cypionate (as ovulatory stimulus) when the NORG ear implants were removed. Timed artificial insemination (TAI) was performed 48h after implant removal and the pregnancy diagnosis was conducted 30 days later. No effects on the P/AI due to PGF2α treatment were observed (PGF2α=51.7 vs. Control=57.7%; P=0.29). In conclusion, PGF2α treatment at the onset of NORG-based protocols for the synchronization of ovulation did not alter the ovarian follicular responses or the P/AI in cyclic Bos indicus beef heifers synchronized for TAI.