Six female Persian onagers (Equus hemionus onager) were treated with fluphenazine decanoate (FD;?0.1?mg/kg IM) or saline control in a random crossover design study.?Urinary cortisol, progesterone, estrogen metabolites and behavior were monitored, and follicular dynamics were examined using ultrasonography until ovulation.?Onagers demonstrated significantly lower cortisol concentrations (P?=?0.03) when treated with FD (6.61?±?3.26?ng/mg creatinine) compared to saline (9.73?±?3.19?ng/mg creatinine).?Overall, there were no differences in peak estrogen (P?=?0.51) or progesterone (P?=?0.38) concentrations between the two groups, and all animals ovulated within the expected time frame following FD treatment.?However, some onagers exhibited only minor reductions in cortisol secretion and one treated female demonstrated a suppressed luteal progesterone peak, indicating a possible reproductive cost to FD administration[1].