Double-Ovsynch in high-producing dairy cows: effects on progesterone concentrations and ovulation to GnRH treatments.

Previous studies reported increased fertility using Ovsynch for presynchronization before Ovsynch (Double-Ovsynch), as compared with presynchronization with two prostaglandin F(2α) (PGF(2α)) treatments before Ovsynch (Presynch-Ovsynch). This study compared ovarian follicular dynamics and hormone concentrations during Double-Ovsynch versus Presynch-Ovsynch. Lactating Holstein cows (N = 193) were assigned to one of two treatment groups: (1) Presynch (N = 93), two injections of PGF(2α) 14 days apart, followed by the Ovsynch-timed AI protocol 12 days later; and (2) Double-Ovsynch (N = 100), one injection of GnRH, PGF(2α) 7 days later, and GnRH 3 days later, followed by the Ovsynch-timed AI protocol 7 days later. All cows received the same Ovsynch-timed AI protocol: GnRH (G1) at 68 ± 3 days in milk (mean ± SEM), PGF(2α) 7 days later, and GnRH (G2) 56 hours after PGF(2α). Ultrasonographic evaluations of the ovaries and blood sampling were performed at G1, PGF(2α), G2, and 6 days after the G2 injection of the Ovsynch-timed AI protocol. Double-Ovsynch decreased the percentage of cows with low circulating progesterone (P4) concentrations (<0.50 ng/mL) at G1 (12.0% vs. 30.1%; P = 0.003) and increased the percentage of cows with medium P4 concentrations (0.50 > P4 ≤ 3.0 ng/mL) at G1 (80.0% vs. 57.0%; P < 0.01), and with CL at G1 (94.0% vs. 67.8%; P < 0.01). Double-Ovsynch also increased the percentage of cows with high P4 (>3.0 ng/mL) at PGF(2α) (88.0% vs. 76.3%; P = 0.04) and tended to increase average circulating P4 at PGF(2α) (3.52 ± 0.17 ng/mL vs. 3.09 ± 0.21 ng/mL; P = 0.11). Double-Ovsynch also tended to increase percentage of cows ovulating to G1 (80.0% vs. 69.9%; P = 0.11) and G2 (98.0% vs. 93.5%; P = 0.08). Thus, presynchronization of cows with Double-Ovsynch induced ovulation in noncycling cows and appeared to increase most aspects of synchronization during the Ovsynch protocol.