171 Follicular and luteal characteristics and pregnancy rates in Bos indicus suckled cows treated with two oestradiol/progesterone-based protocols with a prolonged pro-oestrus

An experiment was designed to evaluate the effect of the length of insertion of a progesterone (P4)-releasing device on follicular and luteal characteristics and pregnancy rates to fixed-time AI (P/FTAI) in Bos indicus cows treated with oestradiol/P4-based treatments with a prolonged pro-oestrus. Multiparous Bos indicus suckled beef cows (n = 659), 60-90 days postpartum, with a corpus luteum (CL) or at least one follicle ≥8 mm in diameter and with a body condition score between 2 and 3.5 (1-to-5 scale) were synchronised using three treatments. On Day 0, all cows received 2 mg of oestradiol benzoate (Sincrodiol, Ourofino) and an intravaginal device with 1 g of P4 (Sincrogest, Ourofino). The P4 device was removed on Day 6 in cows in the J-Synch 6 group (n = 195) and on Day 7 in cows in the J-Synch 7 group (n = 262) and conventional group (n = 202). All cows received 500 μg of cloprostenol (Sincrocio, Ourofino) and 400 IU of equine chorionic gonadotrophin (SincroeCG 6000UI, Ourofino) at the time of P4 device removal. Cows in the conventional treatment group also received 0.5 mg of oestradiol cypionate (SincroCP, Ourofino) at the same time. In addition, all cows were tail-painted for oestrous detection (CeloTest, Biotay). Cows that had lost ≥50% of the tail paint 62-66 h (J-Synch groups) or 48-52 h (conventional group) after device removal were FTAI at that time. Cows not showing oestrus by 62-66 h (J-Synch groups) or 48-52 h (conventional group) received 10 μg of GnRH (Sincroforte, Ourofino) at the same time and were FTAI 8 h later. A subset of 20 cows per group was also examined using ultrasonography (Mindray DP50 Vet) every 12 h from the time of device removal to determine the time of ovulation, 6 days after ovulation to determine CL diameter, and 30 days after FTAI to determine P/AI. Data were analysed using the GLM Mixed procedure (InfoStat). The results are shown in Table 1. The diameter of the dominant preovulatory follicle was larger and the interval from device removal to ovulation was longer in cows in the J-Synch groups compared with those in the conventional group (P < 0.05). Furthermore, the diameter of the CL was larger and P/FTAI was higher in cows in the J-Synch 7 group compared with those in the J-Synch 6 and conventional groups. In conclusion, delaying the removal of the P4 device by 1 day (i.e. Day 7 vs. Day 6) in the J-Synch groups and prolonging the pro-oestrus period by not giving oestradiol cypionate at P4 device removal (i.e. J-Synch 7 vs. conventional) resulted in a larger preovulatory follicle and CL and higher P/FTAI in Bos indicus suckled cows. Table 1.Mean (± s.e.m.) diameter of the preovulatory follicle (P/Foll) and corpus luteum (CL), interval from progesterone (P4) device removal to ovulation, and pregnancy rates to fixed-time AI (P/FTAI) in Bos indicus suckled cows Treatment P/Foll diameter, mm CL diameter, mm Interval to ovulation, h P/FTAI, % (n) J-Synch 6 15.5 ± 0.3a 18.7 ± 0.8a 83.0 ± 4.0b 41.0 (80/195)a J-Synch 7 16.4 ± 0.2b 21.9 ± 0.8b 86.0 ± 3.0b 52.0 (136/262)b Conventional 13.8 ± 0.2a 16.8 ± 0.9a 64.0 ± 3.0a 37.1 (75/202)a a,bDifferent superscripts denote differences between means or P/FTAI.