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Induction of Persistent Ovarian Follicular Structures Following Administration of Progesterone near the Onset of Estrus in Dairy Cattle^{1, 2,}

University of Missouri, Columbia 65211

ABSTRACT

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 F₂, 20 multiparous, non-lactating Holstein cows were randomly assigned into three groups: 1 ml ethanol administered i.m. at 12-h intervals for 24 h (n = 6; group 1); 1 mg progesterone administered i.m. at 12-h intervals for 24 h (n = 7; group 2); 2.5 mg 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 2 h from onset of standing estrus for 30 h, 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 (30 h) 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.

¹ Contribution from the Missouri Agricultural Experiment Station Journal Series Number 10475.

² This research was conducted as part of Regional Research Project NC-113, Methods for Improvement of Fertility in Cows Postpartum.

³ Department of Dairy Science.

⁴ Present address: Department of Animal Science, University of Hawaii, Honolulu 96822.

⁵ Department of Veterinary Medicine and Surgery.

⁶ Present address: Department of Food Animals and Equine Medicine, School of Veterinary Medicine North Carolina State University, 4700 Hillsborough Street, Raleigh 27606.