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Human chorionic gonadotropin (hCG) dose response 7 days after synchronization of ovulation in lactating Holstein cows I: Ovulatory response and serum progesterone concentrations.

E. M. Cabrera

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06-23-2020

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Abstract:

T88
Human chorionic gonadotropin (hCG) dose response 7 days after synchronization of ovulation in lactating Holstein cows I: Ovulatory response and serum progesterone concentrations.
E. M. Cabrera*1, M. R. Lauber1, E. M. Peralta1, T. R. Bilby2, P. M. Fricke1. 1Department of Dairy Science, University of Wisconsin-Madison Madison, WI, 2Merck Animal Health Kenilworth, NJ.

Our objective was to assess the effect of treatment with GnRH or 4 increasing doses of human chorionic gonadotropin (hCG) on ovulatory response of a first-wave dominant follicle and subsequent progesterone (P4) concentrations. Lactating Holstein cows (n = 854) were blocked by parity and randomly assigned to receive no treatment (control, C; n = 147), 100 �g of GnRH (Fertagyl, Merck; n = 144), or 1,000 (n = 138), 2,000 (n = 144), 2,500 (n = 142), or 3,300 (n = 139) IU hCG (Chorulon, Merck) 7 d after the second GnRH treatment of an Ovsynch protocol (G2). Ovaries were evaluated with ultrasonography and blood samples were collected immediately before treatment and 7 d later to assess ovulatory response to treatment and serum P4 concentrations. Data were analyzed using the MIXED and GLIMMIX procedures of SAS. Overall, ovulatory response differed (P < 0.01) among treatments and was 5%a, 79%b, 77%b, 88%c, 93%cd, and 96%d for C, GnRH, 1,000, 2,000, 2,500 and 3,300 IU hCG treatments, respectively. Ovulatory response did not differ between parities (primiparous vs. multiparous) within each treatment. Primiparous cows had greater (P < 0.01) serum P4 concentrations 7 d after G2 than multiparous cows (4.1 vs. 3.6 ng/mL), and cows with double ovulation 7 d after G2 had greater (P < 0.01) serum P4 concentrations than cows with single ovulation (4.2 vs. 3.7 ng/mL). Overall, mean serum P4 concentration 7 d after G2 was 3.8 ng/mL and did not differ among treatments. The increase in P4 concentrations from 7 to 14 d after G2 differed (P < 0.01) among treatments and was 3.6a, 5.9b, 5.7b, 6.5bc, 7.0c, and 6.5bc ng/mL for C, GnRH, 1,000, 2,000, 2,500 and 3,300 IU hCG treatments, respectively. In conclusion, cows treated with 1,000 IU hCG or 100 �g GnRH 7 d after G2 had similar ovulatory responses (~78%), whereas cows treated with 2,000, 2,500 and 3,300 IU hCG after G2 had increased ovulatory responses (~92%). The increase in serum P4 concentrations from 7 to 14 d after G2 reflected ovulatory responses to treatments.

Keywords: human chorionic gonadotropin (hCG), ovulation, lactating dairy cow.