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Human chorionic gonadotropin (hCG) dose response 7 days after synchronization of ovulation in lactating Holstein cows II: Pregnancy outcomes and accessory corpus luteum regression.

E. M. Cabrera

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06-23-2020

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Abstract:

T89
Human chorionic gonadotropin (hCG) dose response 7 days after synchronization of ovulation in lactating Holstein cows II: Pregnancy outcomes and accessory corpus luteum regression.
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 pregnancies per artificial insemination (P/AI), pregnancy loss and accessory corpus luteum (CL) regression. 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 using transrectal ultrasonography immediately before treatment and 7 d later to assess ovulatory response to treatment and accessory CL location relative to the existing CL (ipsilateral vs. contralateral), and pregnancy status was evaluated 32 and 74 d after timed artificial insemination (TAI). Data were analyzed using the GLIMMIX procedure of SAS. Overall, primiparous cows had more (P < 0.01) P/AI than multiparous cows at 32 d (57% vs. 48%) and 74 d (52% vs. 43%) after TAI. Overall, treatment did not affect P/AI and was 54%, 49%, 46%, 47%, 57%, and 51% at 32 d and was 48%, 43%, 41%, 44%, 53%, and 46% 74 d after TAI for C, GnRH, 1,000, 2,000, 2,500 and 3,300 IU hCG treatments, respectively. Overall pregnancy loss from 32 to 74 d after TAI did not differ among treatments and was 8%. Cows (n = 108) with bilateral existing or accessory CL due to the Ovsynch protocol or ovulatory treatments were excluded from analyses based on accessory CL location. Overall, regression of accessory CL from 14 to 74 d after TAI for cows that maintained pregnancies differed (P < 0.01) between cows with ipsilateral (31%) vs. contralateral (56%) accessory CL; however, regression of accessory CL did not affect P/AI 74 d after TAI. In conclusion, treatment of lactating Holstein cows with GnRH or hCG 7 d after G2 did not affect P/AI or pregnancy loss, and regression was greater for contralateral than for ipsilateral accessory CL.

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