Abstract #M185

# M185
Dose-frequency of prostaglandin F treatment of dairy cows exposed to presynchronization and either 5- or 7-d Ovsynch program durations: Ovulatory, luteolytic, and pregnancy risks.
Jeffrey S. Stevenson*1, Julie A. Sauls1, Luís G. D. Mendonça1, Benjamin E. Voelz1, 1Kansas State University, Manhattan, KS.

We hypothesized that neither duration of the Ovsynch (OVS) program nor dose-frequency of PGF would change the proportion of cows with complete luteolysis and an additional GnRH treatment administered as part of a presynchronization (PRE) program (Double OVS: GnRH–7 d–PGF–3 d–GnRH) would not alter the proportion of anovulatory cows starting OVS compared with a shorter PRE program with 1 GnRH treatment (PG-3-G: PGF–3 d–GnRH). Lactating Holsteins (n = 405) milked 3 times daily were enrolled in a 2 × 2 × 2 factorial design (8 treatments) before first postpartum AI. Treatments were employed to test ovulatory, progesterone, and pregnancy outcomes to 3 main effects: (1) 2 PRE programs (PG-3-G vs. Double OVS) administered 7 d before OVS; (2) 2 OVS program durations (GnRH-1–5 or 7 d–PGF–24 h–PGF–32 h–GnRH-2–16 h–timed AI); and (3) 2 PGF dose-frequency treatments (2 × 25 mg) 24 h apart vs. 1 dose (1 × 50 mg) of PGF. The PRE treatments of PG-3-G and Double OVS had no effect on the proportion of cows with luteal function (progesterone [P4] > 1 ng/mL) at the onset of the OVS treatments (87.9 vs. 86.2%), respectively. Although ovulation risk was similar after GnRH-1 (65.8 vs. 60.2%), Double OVS cows had greater (P < 0.05) ovulatory responses than PG-3-G after GnRH-2 (95.6 vs. 90%), respectively. Two 25-mg doses of PGF and 1 × 50-mg dose induced complete luteolysis (P4 < 0.4 ng/mL at 72 h) in both OVS durations, but the 1 × 50-mg dose was less (P < 0.05) effective in the 5-d program. More pregnancy per AI (P/AI; 49.2%) tended (P = 0.07) to occur in the PG-3-G cows in 7-d program compared with other treatment combinations (range: 32.4 to 37.4%; OVS × presynch). An OVS × PGF dose-frequency interaction (P = 0.08) resulted in the 1 × 50-mg dosed cows in the 7-d program with the greatest (46.1%) P/AI and the least P/AI (30.6%) occurred in 1 × 50-mg dosed cows in the 5-d program. Complete luteolysis occurred less often in the 5-d program after the 1 × 50-mg dose, but both PGF dose-frequency effectively induced luteolysis in the 7-d program and luteolysis was related to subsequent P/AI.

Key Words: luteolysis, ovsynch duration, PGF dose-frequency