PSV-3 - Ovarian dynamics of Brahman cows submitted to five-day or twelve-day progesterone-based estrus synchronization protocol

The aim of this study was to investigate the ovarian response of Brahman cows submitted to two different estrus synchronization protocols and to determine the estrus response and ovulation time. A total of 153 Brahman cows were randomly assigned to receive one of the following estrus synchronization protocols: 1) CIDR insert and an injection of prostaglandin F2α (25 mg, PGF) on Day -5 and CIDR removal with PGF on Day 0 (CIDR5; n = 77); 2) CIDR insert on Day -12 and an injection of PGF on Day -12, Day -5 and Day 0 upon CIDR removal (CIDR12; n = 76). Estrotect breeding indicator patches were placed on Day 0 and cows were artificially inseminated (AI) 12h after estrus detection; cows not detected in estrus after 96h received TAI coupled with 100 µg of GnRH. Ovarian dynamics were observed during the protocol and follicular diameter were measured every 12h after AI until ovulation. Cows synchronized with CIDR12 had increased follicular diameter (CIDR5, 10.19 ± 0.51 vs. CIDR12, 13.12 ± 0.52 mm; P = 0.01) and decreased serum concentrations of progesterone (CIDR5, 1.68 ± 0.12 vs. CIDR12, 0.81 ± 0.12 ng/ml; P < 0.01) at CIDR removal. The percentage of cows exhibiting estrus did not differ between treatments (CIDR5, 66.2 vs. CIDR12, 64.5%; P = 0.25). No difference was observed in ovulation rate (CIDR5, 94.1 vs. CIDR12, 94.1%; P = 0.6). Time of estrus expression and ovulation time after CIDR removal did not differ (CIDR5, 59.9 ± 2.3 vs. CIDR12, 61.5 ± 2.3h; P = 0.71 and CIDR5, 88.1 ± 2.6 vs. CIDR12, 90.9 ± 2.6h; P = 0.75; respectively). In conclusion, extended length of CIDR with additional PGF increased follicular diameter and decreased concentrations of progesterone but did not influence estrus response and ovulation time in Brahman cows.