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Abstract The objective of this study was to evaluate the impact of early progesterone removal on pregnancy rates to fixed-time artificial insemination (FTAI) in presynchronized beef cows. Postpartum beef cows (n = 922; body condition score = 4.9 ± 0.77; days postpartum = 77.3 ± 20.77 d) from 7 locations were enrolled in a completely randomized design. Within location, cows were stratified by parity and days postpartum before being randomly assigned to 1 of 2 treatments: 1) 7 d 0). Cows received 100 μg of GnRH on d 7 and the CIDR was removed 7 d later, concurrently with a second prostaglandin F2α (PG2) injection (d 14). Cows received a second injection of GnRH and were FTAI 60-66 h after PG2 (d 17); 2) 7 however, CIDR removal and PG2 were performed on d 13, and cows were FTAI 60-66 h after CIDR removal. Ovarian ultrasonography was performed to determine follicle diameter and CL presence at PG2 and FTAI in a subset of cows (n = 40). Estrus detection patches were utilized to evaluate estrus expression between PG2 and FTAI. Pregnancy diagnosis was performed 28-35 d after FTAI. Cows exposed to the 7 however, there were no differences in follicle diameter at FTAI. Cows that expressed estrus tended to have larger follicle diameter at FTAI compared with cows that failed to express estrus (P = 0.10). Follicular growth between PG2 and FTAI, percentage of cows with a corpus luteum at PG2, and ovulation rate were not impacted by treatment (P ≥ 0.56). No differences were determined between treatments for estrus expression (7 7 P = 0.50) or pregnancy rates to FTAI (7 7 P = 0.69). In conclusion, early removal of progesterone did not impact pregnancy rates in presynchronized beef cows. Thus, the 7&6 Synch protocol described herein may be used as an alternative to the conventional 7&7 Synch protocol without compromising fertility.
Burato et al. (Fri,) studied this question.