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
Título alternativoEffect of use of an additional dose of prostaglandine F2α during the protocol of IATF based on estradiol and progesterone on the fertility in holstein lactating anestrous dairy cows
Programa de posgradoZootecnia - FMVZ
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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.