Induction of Persistent Ovarian Follicular Structures Following Administration of Progesterone Near the Onset of Estrus in Dairy Cattle,

The objective of this study was to determine if progesterone administered near the onset of estrus in dairy cows would block the preovulatory surge of LH and result in subsequent persistence of ovarian follicular structures. Following synchronization of estrus with prostaglandin F2α, 20 multiparous, non-lactating Holstein cows were randomly assigned into three groups: 1ml ethanol administered i.m. at 12-h intervals for 24h (n = 6; group 1); 1mg progesterone administered i.m. at 12-h intervals for 24h (n = 7; group 2); 2.5mg progesterone administered i.v. at the onset of standing estrus (n = 7; group 3). Ovarian structures were palpated per rectum on the day of estrus and twice weekly for 14 d. Blood was collected every 2h from onset of standing estrus for 30h, and concentrations of LH and progesterone were determined. Numbers of cows diagnosed with persistent follicles 10 d after estrus were 1 of 6 (group 1), 2 of 7 (group 2), and 5 of 7 (group 3). The preovulatory surge of LH did not occur during the sampling period (30h) for 1 of 6, 7 of 7 and 5 of 7 cows, for groups 1, 2, and 3, respectively, and mean serum concentrations of LH were higher in group 1 than in groups 2 and 3. Serum concentration of progesterone (ng/ml) was higher in group 1 (1.9±.4) than in groups 2 (.9±.4) and 3 (.9±.4) 10 d following estrus. Blocking the preovulatory surge of LH with exogenous progesterone resulted in persistence of ovarian follicles.