For 23-days, 12 intact pony mares were administered daily injections of dexamethasone (6 mares) or sesame oil (6 mares) during the winter anovulatory period. Blood samples were collected daily (beginning the first day of treatment) for 42 days and assayed for progesterone, testosterone, androstenedione, estradiol, and LH. Four of the six sesame oil treated mares exhibited estrous behavior whereas none of the dexamethasone treated mares exhibited estrous behavior (P <.05). Plasma LH, progesterone, and estradiol concentrations were unchanged by the dexamethasone treatment but testosterone concentrations were suppressed (P <.05) and androstenedione concentrations tended (P <.10) to be suppressed by dexamethasone treatment. Therefore, in the presence of suppressed endogenous androgens, estrous behavior during the winter anovulatory season was eliminated.
