The effect of presynchronization with prostaglandin F_(2α) and gonadotropin-releasing hormone simultaneously, 7 d before Ovsynch, compared with Presynch-10/Ovsynch on luteal function and first-service pregnancies per artificial insemination

摘要

Pregnancy per artificial insemination (P/AI) following Ovsynch is optimized when cows ovulate to the first GnRH of Ovsynch. Fertility programs are designed to presynchronize cows to d 6 or 7 of the estrous cycle to increase the chances of ovulation of a first-wave dominant follicle to the first GnRH of Ovsynch. The hypothesis of this experiment was that simplification of a presynchronization program through the combination of PGF_(2α) and GnRH on the same day, 7 d before Ovsynch, would allow for similar P/AI compared with Presynch-10. Lactating dairy cows (n = 432) 41 to 47 d in milk (DIM) were randomly assigned to 2 treatments within parities for first service. Control cows received Presynch-10/Ovsynch consisting of the following: PGF_(2α)-14 d-PGF_(2α)-10 d-GnRH-7 d-PGF_(2α)-56 h-GnRH-16 h-AI. Treated cows received PGF_(2α) and GnRH-7 d-GnRH-7 d-PGF_(2α)-56 h-GnRH-16 h-AI. All cows received a supplemental injection of PGF_(2α) 24 h after the PGF_(2α) of Ovsynch to enhance complete lu-teolysis. All cows received timed AI between 75 and 81 DIM. Blood was collected to assess circulating concentrations of progesterone (P4), and the number and size of corpora lutea (CL) were recorded using ultrasonography on day of PGF_(2α) of Ovsynch. The administration of PGF_(2α) simultaneously with GnRH and 7 d before Ovsynch (PG+G) had similar P/AI at 28 (46 vs. 48%), 35 (43 vs. 43%), 49 (39 vs. 39%), and 77 d post-AI (38 vs. 39%) compared with Presynch-10. No differences were observed in P/AI in primiparous versus multipa-rous cows at 28 (52 vs. 45%), 35 (48 vs. 41%), 49 (45 vs. 37%), and 77 d post-AI (43 vs. 36%). No difference existed between treatments in percentage of cows with functional CL at PGF_(2α) of Ovsynch, total luteal area (mm2), or serum concentrations of P4 at time of PGF_(2α) of Ovsynch, regardless of parity. Number of CL had a tendency to be greater for multiparous PG+G vs. Presynch-10 cows (2.34 ± 0.09 vs. 2.15 ± 0.08) but not in primiparous cows (1.95 ± 0.10 vs. 1.98 ± 0.11). In summary, administering both PGF_(2α) and GnRH on the same day, 7 d before the start of Ovsynch, appears to be a simple and effective alternative to Presynch-10 Ovsynch.