Ultrasonographic study of ovarian function during early pregnancy and after parturition in the ewe

Transrectal ultrasonography of ovaries was performed in 11 ewes from Days 1 0 to 26 and on Day 30 of pregnancy to record the number, size, and position of ovarian follicles greater than or equal to 3 mm in diameter and corpora lutea (CL). Transrectal and/or transabdominal ultrasonography of the uteru s was performed on Days 10 to 26, 30, 35, 40, 45 and 50 of gestation to asc ertain the number and position of the conceptuses. In a second experiment, ultrasonography was conducted in 15 ewes on Days 10, 25, 30, 45 and 50 of p regnancy and from Days 13 to 29 after parturition. Ovarian data were classi fied into ovaries without CL (Group 1), ovaries with the CL in 1 ovary (Gro up 2), and ovaries with the CL in both ovaries during pregnancy (Group 3). In early pregnant ewes, the total number of follicles and the diameter of a ll follicles greater than or equal to 3 mm were smaller (P<0.05) in the CL- bearing ovaries (both Group 2, n=7 and Group 3, n=8) than in the non-CL-bea ring ovaries (Group I,n=7), while the largest follicle diameter was signifi cantly smaller in Group 3 than in Group 1 or 2 ovaries. The number of 3-mm follicles in Group 2 ovaries was lower (P<0.05) than in Group 1 or 3 ovarie s, but the mean number of follicles greater than or equal to 5 mm in diamet er was significantly lower in Group 3 than in Group 1. The total luteal vol ume per ovary was higher (P<0.001) in Group 2 than in Group 3 ovaries of ea rly pregnant ewes. The total follicle diameter and the number of follicles growing from 3 to greater than or equal to 5 mm in diameter was lower (P<0. 05) for Group 2 ovaries of ewes that carried twins (n=3) compared with Grou p 2 ovaries from ewes with singletons (n=4). There were no differences in f ollicular dynamics between Group 3 ovaries and the ovaries of Group 2 in ew es that carried twins. No follicles >3 mm were seen in the ovaries of postp artum ewes that contained CL during gestation, until Days 21 and 25 postpar tum for Groups 2 (n=10) and 3 (n=8), respectively, and follicles reaching g reater than or equal to 5 mm in diameter were detected in only 2 ovaries (G roup 2), on Days 27 and 28 postpartum, respectively. We conclude that durin g early pregnancy in ewes there is a suppression of antral follicle growth which appears to be exerted primarily by the developing conceptus but remai ns confined to CL-bearing ovaries. Residual local inhibition of follicular development extends into the postpartum period. (C) 2000 by Elsevier Scienc e Inc.