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Effect of human chorionic gonadotropin treatment on d 7 or d 7 and 13 of the estrous cycle on luteal and follicular dynamics in non-inseminated lactating Holstein cows.

T. O. Cunha

Events

06-24-2020

Abstract:

402
Effect of human chorionic gonadotropin treatment on d 7 or d 7 and 13 of the estrous cycle on luteal and follicular dynamics in non-inseminated lactating Holstein cows.
T. O. Cunha*1, L. R. Statz1, R. R. Domingues2, J. P. N. Andrade1,2, M. C. Wiltbank2, J. P. N. Martins1. 1School of Veterinary Medicine, University of Wisconsin-Madison Madison, WI, 2Department of Dairy Science, University of Wisconsin-Madison Madison, WI.

Our objective was to determine the effect of human chorionic gonadotropin (hCG; 3,300 IU i.m.) on d 7 (hCG7) or d 7 and 13 (hCG13) of the estrous cycle on ovarian function in lactating Holstein cows. Cows (44.2 � 0.6 DIM) were pre-treated with an Ovsynch+CIDR protocol, and only synchronized cows were used (n = 64). The day of the last GnRH was considered d0 of the estrous cycle. Follicular and luteal dynamics of cows were evaluated daily during an entire estrous cycle by ultrasound. Blood samples were collected daily to measure serum concentration of progesterone (P4). Cows were randomly assigned to CON (n = 22, no treatment), hCG7 (n = 20), or hCG13 (n = 22) treatments. Only cows that ovulated by 2d after hCG treatments were used in the study (n = 62). The first day of luteolysis was considered the day that P4 declined to < than 2x the SD of the mean for the 4 highest P4 levels in late diestrus. The P4 cut-off for complete luteolysis was <1.0 ng/mL. Mean P4 (3.20 � 0.16 ng/mL) did not differ (P = 0.48) between treatments on d7. Cows treated with hCG had greater (P < 0.01) P4 between d 8 and 15 of the cycle than CON. Cows treated with hCG13 had greater (P < 0.02) P4 on d 14 and 15 of the cycle than hCG7. Cows were classified as atypical if the dominant follicle (DF) or future DF at the time of luteolysis did not ovulate (CON, n = 2; hCG7, n = 4; hCG13, n = 3), had a short cycle (CON, n = 1), delayed (CON, n = 2) or incomplete luteolysis (CON, n = 1; hCG7, n = 4; hCG13, n = 5). Most cows with incomplete luteolysis (n = 9/10) had at least 2 ipsilateral CL in one ovary, and 1 or 2 CL did not regress. Proportion of cows with typical cycle were 73% (16/22) for CON, 60% (12/20) for hCG7, and 60% (12/20) for hCG13. Typical cycle cows treated with hCG had delayed (P ≤ 0.03) luteolysis, prolonged time (P < 0.01) to undergo complete luteolysis, and more cows with 3 follicular waves (P < 0.01; hCG7 = 92%; hCG13 = 100%; CON = 25%) than CON; resulting in a longer interovulatory interval (P < 0.01) for hCG7 (24.9 d � 0.4) and hCG13 (26.0 d � 0.7) than CON (22.0 d � 0.5). In summary, hCG treatments had an effect not only on the follicular and luteal dynamics but also on the luteolysis process.

Keywords: human chorionic gonadotropin (hCG), corpus luteum, luteolysis.