The effect of presynchronization with prostaglandin F2α and gonadotropinreleasing hormone simultaneously, 7 d before Ovsynch, compared with Presynch-10/0vsynch on luteal function and first-service pregnancies per artificial insemination

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(2 alpha) 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(2 alpha)-14 d PGF(2 alpha)-10 d-GnRH-7 d-PGF(2 alpha)-56 h-GnRH-16-hAI. Treated cows received PGF(2 alpha) and GnRH-7 d GnRH-7 d PGF(2 alpha)-56 h-GnRH-16 h-AI. All cows received a supplemental injection of PGF(2 alpha) 24 h after the PGF(2 alpha) of Ovsynch to enhance complete luteolysis. 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(2 alpha) of Ovsynch. The administration of PGF(2 alpha) 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 multiparous 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 PGF2, of Ovsynch, total luteal area (mm(2)), or serum concentrations of P4 at time of PGF2c, 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(2 alpha) 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.