Dose frequency of prostaglandin F2α administration to dairy cows exposed to presynchronization and either 5-or 7-day Ovsynch program durations: Ovulatory and luteolytic risks

We hypothesized (1) that neither duration of the Ovsynch program nor dose frequency of PGF(2 alpha )would change the proportion of cows with complete luteolysis (progesterone <0.4 ng/mL 72 h after PGF(2 alpha)) and (2) that the additional GnRH treatment administered as part of a presynchronization program would not alter the proportion of anovulatory cows starting the timed artificial insemination (AI) program compared with an alternative shorter presynch program including only 1 GnRH treatment. Lactating Holstein cows (n = 406) were milked 3 times daily and enrolled in a 2 x 2 x 2 factorial experiment consisting of 8 treatments before the first postpartum AI. Treatments were used to test ovulatory, luteal, and luteolytic outcomes to 3 main effects: (1) 2 GnRH-PGF(2 alpha) presynchronization programs (PG-3-G vs. Double Ovsynch), (2) 2 Ovsynch program durations [5 d: GnRH (GnRH-1)-5 d-PGF(2 alpha)-24 h-PGF(2 alpha)-32 h-GnRH (GnRH-2)-16 h-timed AI; 7 d: GnRH-1-7 d-PGF(2 alpha)-56 h-GnRH-2-16 h-timed AI], and (3) 2 PGF(2 alpha) dose frequency treatments (2 x 25 mg) 24 h apart versus 1 dose (1 x 50 mg) of PGF(2 alpha) administered 72 h before timed AI. The presynchronization treatments of PG-3-G and Double Ovsynch had no effect on the proportion of cows with luteal function at the onset of the Ovsynch treatments (87.9 vs. 86.2%). Although ovulatory responses were similar after GnRH-1 (>60%), Double Ovsynch cows tended to have greater ovulatory responses than PG-3-G after GnRH-2 (95.3 vs. 90.6%). The 2 x 25-mg doses of PGF(2 alpha) and the 1 x 50-mg dose induced luteolysis in both Ovsynch treatment durations, but the 1 x 50-mg dose was less effective in the 5-d program. More pregnancy per AI (P/AI; 49.2%) tended to occur in the PC-3-G cows in the 7-d program compared with the other treatment combinations (range: 32.4-37.4%; Ovsynch x presynch interaction). In addition, an Ovsynch x PGF(2 alpha) dose frequency interaction resulted in cows receiving the 1 x 50-mg dose in the 7-d program having the greatest P/AI (46.1%) and cows receiving the 1 x 50-mg dose in the 5-d program having the least P/AI (30.6%). We conclude that complete luteolysis was less effective in the 5-d program when the 1 x 50-mg dose was applied, but both PGF(2 alpha) dose frequencies (1 x 50 mg and 2 x 25 mg 24 h apart) effectively induced complete luteolysis in the 7-d program. Treatments producing complete luteolysis tended to be related to subsequent pregnancy outcomes.