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Effects of additional prostaglandin F₂ and estradiol-17β during Ovsynch in lactating dairy cows

Department of Dairy Science, University of Wisconsin, Madison 53706

¹ Corresponding author: wiltbank{at}wisc.edu

This study was designed to evaluate whether decreasing circulating progesterone (P4) or increasing circulating estradiol-17β (E2) near the time of artificial insemination (AI) in an Ovsynch protocol would increase pregnancies per AI (P/AI) in lactating dairy cows. Six hundred nineteen lactating Holstein cows (n = 772 inseminations) received Ovsynch (GnRH–7 d–PGF₂–56 h–GnRH–16 h–timed AI). Cows were randomized in a 2 x 2 factorial experiment of 4 treatments to receive or not receive 25 mg of PGF₂ 24 h after the standard PGF₂ of Ovsynch, or 0.5 mg of E2 at the time of the final GnRH of Ovsynch, or both. Blood samples were collected 24 h after normal PGF₂ and at final GnRH to evaluate circulating P4. Ovarian ultrasound was done at final GnRH to determine preovulatory follicle size. Ovulation was confirmed by ultrasound 5 d after AI. Treatment with additional PGF₂ increased the percentage of cows that had complete luteal regression (95.6%) compared with control cows (84.6%). In contrast, additional PGF₂ had no detectable effect on P/AI (control = 41.5% vs. + PGF₂ = 44.7%). Supplementation with E2 increased expression of estrus (84.4 vs. 37.2%), but had no effect on overall fertility and even tended to have a negative effect on fertility in cows that ovulated to the second GnRH (control = 51.5% vs. +E2 = 44.0%). Thus, additional treatments with PGF₂ or E2 during Ovsynch can be used to increase synchronization and expression of estrus during Ovsynch, although the lack of improvement in fertility makes these treatments unwarranted.

Key Words: additional prostaglandin F₂ • estradiol • Ovsynch