Efeito do uso de uma dose adicional de prostaglandina F2α durante o protocolo de IATF à base de estradiol e progesterona na fertilidade de vacas holandesas em lactação em anestro

Abstract

The objectives of these experiments were to determine the effects of a second prostaglandin F2α (PGF2α) dose in an estradiol (E2) and progesterone (P4) based timed AI (TAI) protocol on LH pulsatility, pre-ovulatory follicle characteristics, and pregnancy per AI (P/AI) in anestrous lactating Holstein cows. In experiment 1, 2,011 Holstein cows had their estrous cycles synchronized and ovaries scanned by ultrasound to determine if a corpus luteum (CL) was present at the time of protocol initiation (d-12) and on the day of PGF2α (d-4). Cows without CL on d-12 and d-4 were classified as anestrous (n = 454) and submitted to the following TAI protocol: d -12 or -11: two intravaginal P4 devices and estradiol benzoate (EB); d -4 PGF2α and withdrawal of one P4 device; d -2 estradiol cypionate (ECP) and withdrawal of the second P4 device; on d 0, TAI was performed. On d -4, cows were randomly assigned to one of four treatments: one dose of PGF2α on d -4 and 9 days with a P4 device (1PGF9d, n = 116); two doses of PGF2α, the first on d -4 and the second on d -2 and 9 days with a P4 device (2PGF9d, n = 115); one dose of PGF2α on d -4 and 10 days with a P4 device (1PGF10d, n = 111) or two doses of PGF2α, the first on d -4 and the second on d -2 and 10 days with a P4 device (2PGF10d, n = 112). Rectal temperature (RT) was measured on d 0 and 7 and cows were classified as RT below (normothermic) or above 39.0oC (hyperthermic). Pregnancy was diagnosed on d 30 and 58 after AI. In experiment 2, 56 Holstein cows had the estrous cycle synchronized to start the timed AI without a CL. All cows were assigned to an E2/P4 based protocol synchronization. On d -11, cows were blocked by milk yield and parity and randomly assigned to 1PGF, 5 mL of saline on d -2; or 2PGF, a second dose of 25 mg of dinoprost on d -2. Blood was sampled from d -11 to 0 and assayed for P4. Jugular catheters were placed and blood was sampled every 15-min from 1 h before to for 6 h after treatments, and every 2 h thereafter for 58 h. Plasma samples were assayed for concentrations of LH and PGF2α metabolite (PGFM). The pre-ovulatory follicle was aspirated on d 0 and fluid assayed for E2 and P4. In experiment 1, protocol using 9 or 10 days with P4 device did not alter P/AI at 30 d (15.8 vs. 18.2%; P = 0.50) and 58 d (13.9 vs. 16.2%; P = 0.51). 2PGF increased (P = 0.04) ovulation after AI in all cows (75.3 vs. 83.1%). Also, in cows with RT ≤ 39.0, 2PGF increased (P < 0.03) P/AI on 58d in all inseminated cows (15.7 vs. 30.7%) or only synchronized cows (19.5 vs. 35.1%), but not in cows with RT > 39.0 (all inseminated cows, 10.0 vs. 9.5%; only synchronized cows, 14.8 vs. 12.2%). In experiment 2, 2PGF reduced (P = 0.05) the number of LH pulses/6 h (4.5 vs. 3.9 ± 0.2). Relative to treatment, the beginning of LH surge (22.4 vs. 19.3 ± 2.1 h), the hour when the peak of LH surge was detected (29.0 vs. 28.0 ± 1.8 h), and LH peak (4.1 vs. 3.7 ± 0.3 ng/mL) did not differ between 1PGF and 2PGF, but duration of the surge was longer (P = 0.04) for 2PGF than 1PGF (13.1 vs. 15.5 ± 0.8 h). Cows in 2PGF had larger (P = 0.05) pre-ovulatory follicle diameter (12.3 vs. 14.4 ± 0.8 mm) with greater (P = 0.02) estradiol concentration in the follicular fluid in all aspirated follicles (115 vs. 262 ± 39 ng/mL) or in estrogenic follicles (161 vs. 372.8 ± 28 ng/mL). Treatment with a second dose of PGF2α improved P/AI in normothermic anovular cows because of increased ovulation and improved pre-ovulatory follicle characteristics.