EFFECTS OF BROMOCRIPTINE TREATMENT ON THE EXPRESSION OF SEXUAL-BEHAVIOR IN MALE SHEEP (OVIS-ARIES)

Twenty-three rams were treated twice daily with subcutaneous injection s of bromocriptine or vehicle over 30 d during two seasons, spring and fall. Sexual behavior was observed and quantified to determine the ef fects of bromocriptine-induced hypoprolactinemia on mount attempt (MA) , mount (M), and ejaculation (E) frequency of the rams upon exposure t o estrous ewes. Behavioral responses and serum prolactin (PRL) concent rations were determined on a weekly basis before, during, and after th e treatment period in each season. Treatment with bromocriptine caused a significant decrease in serum concentrations of PRL during both sea sons (P < .01). Post-treatment period concentrations of PRL returned t o pretreatment levels during the spring,;whereas during the fall, post -treatment period PRL concentrations remained low (P < .05). The frequ ency of MA and M was lower during bromocriptine treatment relative to control rams in the spring (P < .05). The frequency of MA and M return ed to pretreatment values after bromocriptine treatment was withdrawn. Ejaculation frequency tended to decrease during and after bromocripti ne treatment relative to controls (P < .09). There was no effect of br omocriptine treatment on frequency of MA and M during the fall. During the fall, the frequency of E tended to decrease in bromocriptine-trea ted rams (P < .1). These data indicate that bromocriptine-induced hypo prolactinemia is associated with a significant diminution in expressio n of sexual behavior in rams. It is suggested that PRL modulates the i ntensity of expression of sexual behavior in rams, and this effect may be season-dependent.