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

作者：Carvalho P D; Wiltbank M C; Fricke P M^*

来源：Journal of Dairy Science, 2015, 98(12): 8800-8813.

DOI：10.3168/jds.2015-9968

• progesterone
• timed artificial insemination
• fertility

Ovulation to the first GnRH (G1) treatment of the Ovsynch protocol improves synchronization rate and pregnancies per AT (P/AI). Elevated progesterone (P4) concentrations at Cl decrease the ovulatory response by deereasing 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 Cl 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, PGF(2 alpha); d 10, GnRH) followed 7 d later by an Ovsynch-56 protocol (d 0, G1; d 7, PGF(2 alpha); d 8, PGF2a; d 9.5, GnRH)] to receive first timed artificial insemination (TAI; 80 +/- 3 DIM) 16 h after the last GnRH treatment. Cows were randomly assigned to receive 12.5 mg of PGF(2 alpha) (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 Cl compared with low-P4 cows (3.0 vs. 1.3 ng/mL, respectively). Ovulatory response to Cl 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/AT 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 Cl 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 Cl (16.4%) combined with the observed increase in ovulation to Cl 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 PGF(2 alpha) 2 d before G1 during a Double-Ovsynch protocol decreased P4 at G1 and increased ovulatory response to G1.

• 出版日期2015-12