Lengthening the Bovine Estrous Cycle with Low Levels of Exogenous Progesterone: A Model for Studying Ovarian Follicular Dominance*

作者：Jean Sirois, J. E. Fortune · 发表于：Endocrinology · 年份：1990 · DOI：10.1210/endo-127-2-916 · 被引用次数：373 · 研究领域：Reproductive Physiology in Livestock、Reproductive Biology and Fertility、Genetic and phenotypic traits in livestock

In cattle the development of ovarian follicles greater than or equal to 5 mm occurs in waves, with either two or three waves per estrous cycle. To increase our understanding of the control of follicular dynamics in cattle, the present study was designed to characterize the pattern of follicular development during artificially lengthened estrous cycles. Cycles were lengthened by intravaginal insertion of Silastic devices containing progesterone [Controlled Internal Drug Release devices (CIDRs)]. Control heifers (group 1) received blank devices, whereas treated heifers received one (group 2) or two CIDRs (group 3) from days 14 to 28 after estrus. In groups 2 and 3, the insertion of CIDRs prevented return to estrus at the normal time and increased cycle length as compared to the control group (30.0 +/- 0.0 and 31.0 +/- 0.3 vs. 21.0 +/- 0.7 days, respectively, P less than 0.05). After natural luteolysis and between days 22 and 28 of cycle, progesterone concentrations were maintained at lower levels in group 2 (range = 0.9-2.1 ng/ml) than in group 3 (range = 3.7-4.9 ng/ml, P less than 0.003). Follicular development and regression were monitored daily by ultrasonography. The number of follicular waves per cycle was identical in groups 1 and 2 (2.7 waves per cycle), despite the significantly longer cycles in group 2. In group 2, the presence of one CIDR altered the normal pattern of follicular development by promoting the prolonged growth of the ovulatory follicle, and associated wi...