Master of Science (MS)


School of Animal Science

Document Type



An experiment was conducted to determine the effects of dihydrotestosterone (DHT) and estradiol benzoate (EB) given simultaneously on concentrations of FSH and LH and the associated follicular activity, and to monitor the subsequent recovery of the gonadotropes and follicular growth following treatment with either DHT or EB. Twelve mares were assigned to daily treatments of DHT (150 Fg/kg BW) plus EB (22 Fg/kg BW) from d 0 through 30 (Phase I). Beginning on d 31, mares were randomly assigned to one of three treatment groups: 1) oil, 2) DHT (150 Fg/kg BW), or 3) EB (22 Fg/kg BW). On d 30, 44, and 58, GnRH was administered to determine the response of FSH and LH. In phase I, DHT plus EB decreased (P = 0.0001) concentrations of LH and FSH. In phase II (d 31 to 66), DHT decreased (P = 0.0001) LH and FSH concentrations. Estradiol benzoate decreased (P= 0.0001) concentrations of FSH but increased (P = 0.0001) concentrations of LH. There was a significant treatment x day x minute interaction of FSH (P = 0.0001) and LH (P = 0.0002) concentrations in response to administration of GnRH on d 30, 44, and 58. The number of medium follicles (P = 0.0001), large follicles (P = 0.0012) and the size of the largest follicle per day (P = 0.0001) decreased during phase I. During phase II, there was a treatment x day interaction (P = 0.0001) for medium follicles and large follicles. Control mares had more large follicles on d 57 through d 63 whereas EB treated mares had more large follicles on d 45, 49, and 51. Control mares had increased size of the largest follicles at d 57 to 63. Mares in the DHT and EB groups had prolonged (P = 0.01) ovulation intervals as compared with controls. It is concluded that the combination of DHT plus EB suppresses gonadotropin concentrations and the associated follicular activity in mares. Also, concentrations of both gonadotropins must be restored to normal for growth of an ovulatory size follicle and the subsequent ovulation of that follicle.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Donald L. Thompson, Jr.