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Journal of Animal Science, Vol 71, Issue 11 3067-3072, Copyright © 1993 by American Society of Animal Science
JOURNAL ARTICLE |
J. A. Hall, R. A. Dailey, E. K. Inskeep and P. E. Lewis
Division of Animal and Veterinary Sciences, West Virginia University, Morgantown 26506-6108.
This study was conducted to determine the effects of the corpus luteum (CL) of pregnancy and(or) the previously gravid uterine horn (g-UH) on the incidence and site of ovulation and the duration of luteal function in postpartum (PP) ewes. Ewes were laparotomized at d 60 to 80 of gestation and assigned to one of four groups: 1) single g-UH, CL left intact (SI, n = 35); 2) single g-UH, CL removed (SR, n = 30); 3) twin g-UH, CL on both ovaries left intact (TI, n = 21); and 4) twin g-UH, CL removed from one ovary (TR, n = 32). On d 20 PP, the number of follicles on each ovary was determined at laparoscopy, and ewes received (i.m.) 750 IU of hCG. Ovarian structures were determined at laparoscopy on d 24 PP. Blood samples were collected daily from d 20 to 40 PP and assayed for progesterone. more follicles (P < .05) were observed at laparoscopy on d 20 PP in SI/TI than in SR/TR groups (8.4 vs 6.0, respectively; SE = .4). Overall, 52% of the ewes had visible CL 4 d after hCG, and 73% of the ewes had elevated levels of progesterone by 7 d after hCG. The number of g-UH (S vs T) or status of the CL (I vs R) did not affect these responses. For SR ewes with hCG-induced CL on a single ovary, the incidence of CL formation on the ovary adjacent to g-UH was less (P < .05) than that for SI ewes (0 vs 57, respectively). Removal of the CL from S ewes, but not from T ewes, reduced follicular development and ovulation in response to hCG. Perhaps there is a positive systemic effect of the CL of pregnancy on postpartum ovarian function in ewes.
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