Comparison of Follicular and Luteal Dynamics in Protocols Developed for Synchronization of Ovulation in Bos indicus-Influenced Beef Cows: The Role of Gonadotropin-Releasing Hormone at Treatment Onset
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The 5-day Bee Synch + CIDR (Bee Synch) protocol for Bos indicus-influenced cows utilizes CIDR, GnRH (GnRH-1) and PGF on day 0 to eliminate mature corpora lutea, with FTAI and GnRH (GnRH-2) at 66 hours after CIDR removal to yield pregnancy rates of ~ 50%. The objective was to test the hypothesis that GnRH-1 is not required to optimize follicle synchrony. Seventy-one cycling Brangus and Brahman × Hereford suckled cows were used in 2 replicates (35-36 per replicate). Cows were stratified by BW, BCS, and days postpartum, and assigned randomly in a 2 × 3 factorial arrangement involving 2 truncated (no FTAI or GnRH-2) versions of Bee Synch (BS-I and II) begun 3, 7 and 10 days post ovulation. Ovulation was pre-synchronized with PGF. Cows in BS-I received 100 µg GnRH i.m., 25 mg PGF i.m., and a CIDR on treatment onset. Cows in BS-II did not receive GnRH-1. On day 5, CIDRs were removed and all cows received 50 mg PGF i.m. Estrus was detected with Estrotect patches. Daily ultrasonography confirmed ovulation. Synchronized new follicular wave emergence (NFWE; days 1-4) was observed in 68.6 and 38.9% (BS-I vs. BS-II; P = 0.01) of cows and increased to 93.3 and 72.2%, respectively, if days 0-4 were considered. Size of the largest follicle at 66 hours (13.5 ± 0.47 mm) did not differ by treatment or day post ovulation. Interval from CIDR removal to ovulation was greater (P = 0.02) for BS-I (5.2 ± 0.2 days) than BS-II (4.4 ± 0.2 days) and greater (P < 0.0001) for day 3 (6.35 ± 0.3 days) than days 7 and 10 (4.31 ± 0.3 and 3.7 ± 0.3, respectively). Progesterone concentrations did not differ between treatments (P = 0.12). The LH peak at 120 minutes after GnRH-1 was higher (4.28 ± 0.71 ng/mL, P < 0.05) for day 3 than days 7 and 10. A greater (P = 0.06) proportion (15.5%) of cows in BS-II ovulated by 72 hours than in BSI. GnRH-1 reduced variation in day to NFWE and incidence of early ovulations.
De Souza Scarpa, Jose Oswaldo (2018). Comparison of Follicular and Luteal Dynamics in Protocols Developed for Synchronization of Ovulation in Bos indicus-Influenced Beef Cows: The Role of Gonadotropin-Releasing Hormone at Treatment Onset. Master's thesis, Texas A & M University. Available electronically from