117 Effect of length of insertion of a progesterone device on follicular diameter, time of ovulation, and pregnancy rates in Bos indicus cows treated with an oestradiol/progesterone-based protocol with a prolonged proestrus

Abstract

Three experiments were designed to evaluate the effect of the length of insertion of a intravaginal progesterone (P4) device on follicular and corpus luteum (CL) diameter, time of ovulation, and pregnancy rates following fixed-time AI (P/FTAI) in Bos indicus cows treated with an oestradiol/P4-based treatment with a lengthened proestrus, named J-Synch. Multiparous suckled Bos indicus beef cows that were 35 to 60 days postpartum were used in Experiments 1 and 2, whereas non-lactating cows were used in Experiment 3. All cows had a CL or a follicle of at least 8 mm in diameter and a body condition score between 2.5 and 4 (1 to 5 scale) at the time of treatment. On Day 0, all cows received 2 mg of oestradiol benzoate (EB; Sincrodiol, Ourofino, Brazil) and a previously used intravaginal device (1 g of P4; Sincrogest, Ourofino). The P4 device was removed on Day 6 in the J-Synch 6-day group and on Day 7 in the J-Synch 7-day and Control groups. All cows received 500 µg of cloprostenol (Sincrocio, Ourofino) and 400 IU of equine chorionic gonadotrophin (SincroeCG, Ourofino) at the time of P4 device removal, and cows in the Control group also received 0.5 mg of oestradiol cypionate (ECP, SincroCP, Ourofino) at the same time. In Experiment 1, cows (n = 20 per group) were examined every 12 h, from P4 device removal to determine the time of ovulation and 7 days after ovulation to measure the CL. In Experiment 2, all cows (n = 200 per group) were tail-painted for oestrous detection. Cows with = 50% of the tail-paint rubbed-off by 72 h (J-Synch groups) or 48 h (Control group) after P4 device removal, were FTAI at that time. Cows not designated as showing oestrus at that time received 10 µg Buserelin (GnRH, Sincroforte, Ourofino) and were FTAI 8 h later. In Experiment 3, P/FTAI was compared in cows that received the J-Synch 7-day treatment (n = 265) or the 7-day Control treatment (n = 250). Data were analysed using the GLM mixed procedure (InfoStat). In Experiment 1, the diameter of the ovulatory follicle was larger (P < 0.05) and the interval to ovulation was longer (P < 0.05) in the J-Synch groups (J-Synch 7 d: 16.4 ± 0.2 mm and 86.0 ± 3.0 h; J-Synch 6 d:15.5 ± 0.3 mm and 83.0 ± 4.0 h) than in the Control group (13.8 ± 0.2 mm and 64.0 ± 3.0 h). Furthermore, CL diameter was greater (P < 0.05) in the J-Synch 7-day group (21.9 ± 0.8 mm) than in the J-Synch 6-day (18.7 ± 0.8 mm) and Control (16.8 ± 0.9 mm) groups. In Experiment 2, P/FTAI was higher (P < 0.05) in the J-Synch 7-day group (116/200; 58.0%) than in the J-Synch 6-day (93/200; 46.5%) and Control (98/200; 49.0%) groups. In Experiment 3, P/FTAI was higher (P < 0.05) in the J-Synch 7-day group (161/265; 60.7%) than in the Control group (124/250; 49.6%). In conclusion, delaying the removal of the P4 device by 1 day (i.e. Day 7 vs. Day 6) in the J-Synch protocol and lengthening the proestrous period (i.e. J-Synch 7-day vs. 7-day Control) resulted in higher P/FTAI in Bos indicus cows.