title: Manipulation of progesterone to increase ovulatory response to the first GnRH treatment of an Ovsynch protocol in lactating dairy cows receiving first timed artificial insemination.
abstract: Ovulation to the first GnRH (G1) treatment of the Ovsynch protocol improves synchronization rate and pregnancies per AI (P/AI). Elevated progesterone (P4) concentrations at G1 decrease the ovulatory response by decreasing the magnitude of the GnRH-induced LH surge. Therefore, our objective was to evaluate the effect of temporarily decreasing P4 concentrations before initiation of an Ovsynch protocol on ovulatory response to G1 and P/AI. Lactating Holstein cows (n=800) at 53±3 (herd A) or 51±3 (herd B) d in milk (DIM) were synchronized using a modified Double-Ovsynch protocol [pre-Ovsynch protocol (d 0, GnRH; d 7, PGF2α; d 10, GnRH) followed 7 d later by an Ovsynch-56 protocol (d 0, G1; d 7, PGF2α; d 8, PGF2α; d 9.5, GnRH)] to receive first timed artificial insemination (TAI; 80±3 DIM) 16h after the last GnRH treatment. Cows were randomly assigned to receive 12.5mg of PGF2α (a half-dose of dinoprost tromethamine) 2 d before G1 (low-P4) or serve as untreated controls (high-P4). Overall, high-P4 cows had greater P4 concentrations at G1 compared with low-P4 cows (3.0 vs. 1.3ng/mL, respectively). Ovulatory response to G1 was greater for low-P4 than high-P4 cows [81.1 vs. 60.3%, respectively]. Premature luteal regression during the second Ovsynch protocol did not differ between treatments [15.0% vs. 10.7%; for low-P4 vs. high-P4 cows, respectively]. Overall, P/AI did not differ between treatments 32 d after TAI [56.3 vs. 52.9%, for low-P4 vs. high-P4 cows, respectively] or 67 d after AI [50.5 vs. 47.6%, for low-P4 vs. high-P4 cows, respectively]. Pregnancy loss from 32 to 67 d after TAI did not differ between treatments [9.9 vs. 9.3%, for low-P4 vs. high-P4 cows, respectively]. Overall, cows that ovulated to G1 had more P/AI than cows that did not ovulate [58.2 vs. 41.8%, respectively]. The increase in P/AI for cows that ovulated to G1 (16.4%) combined with the observed increase in ovulation to G1 due to treatment (20.8%; low-P4 - high-P4) resulted in the expected numerical increase in P/AI of 3.4% in low-P4 versus high-P4 cows observed in this experiment. We conclude that administration of a half-dose of PGF2α 2 d before G1 during a Double-Ovsynch protocol decreased P4 at G1 and increased ovulatory response to G1.
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706.
authors.forename: P D
authors.initials: PD
authors.lastname: Carvalho
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706.
authors.forename: M C
authors.initials: MC
authors.lastname: Wiltbank
authors.affiliation: Department of Dairy Science, University of Wisconsin, Madison 53706. Electronic address: pmfricke@wisc.edu.
authors.forename: P M
authors.initials: PM
authors.lastname: Fricke
mesh_terms: D000034:Abortion, Veterinary; D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation / Q000502:physiology; D003341:Luteolysis / Q000187:drug effects; D008892:Milk / Q000187:drug effects; D010060:Ovulation / Q000187:drug effects* / Q000502:physiology; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary; D011247:Pregnancy; D011374:Progesterone / Q000097:blood*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D015237:Dinoprost
keywords: fertility; progesterone; timed artificial insemination