Influence of castration and estrogen replacement on sexual behavior of female-oriented, male-oriented, and asexual rams

An experiment was conducted to determine whether exogenous estradiol-17 bet a (E-2) could restore sexual behavior in castrated rams. The protocol consi sted of three sequential 6-wk periods during which rams were studied while 1) intact, 2) bilaterally castrated, or 3) implanted s.c. with two 7.6-cm s ilastic implants each containing 309 +/- 16 mg of E-2. Rams (classified as female-oriented [FOR, n = 7], male-oriented [MOR, n = 7], or asexual [n = 7 ]) were subjected to 30-min sexual behavior tests every 2 wk during the ens uing 18 wk. Rams were observed for mounts and ejaculations using two ovarie ctomized, estrous ewes and two intact males secured in stanchions. Behavior al data were analyzed using the signed rank test, but asexual rams showed n o sexual behavior and therefore were not evaluated statistically. Jugular b lood was collected prior to castration and at the end of the 18-wk period, and testicular venous (n = 21) and arterial (n = 8) bloods were collected i mmediately prior to castration. Radioimmunoassay was used to quantify syste mic levels of estrone (E-1), E-2, and testosterone (T) and testicular serum concentrations of oxytocin (OT). Mounting behavior of MOR and FOR declined after castration (P < .05 and P < .10, respectively). Castration reduced t he number of ejaculations by FOR (P < .05), but not by MOR (P > .10). Mount ing behavior of castrated MOR and FOR was not affected by E-2 treatment rel ative to that observed if castrated only (P > .10). Treatment of asexual ra ms with E-2 did not stimulate sexual behavior in these rams. There were no marked differences (P > .10) among ram groups with regard to serum concentr ations of E-1, E-2, or T prior to castration (overall mean +/- SE, 12.8 +/- .7, 7.6 +/- .5, and 2,670 +/- 780 pg/mL, respectively) or any difference ( P > .10) in systemic concentration of E-1 or E-2 among ram groups after ram s were implanted with E-2 (overall mean +/- SE, 9.7 +/- .7 and 9.0 +/- .7 p g/mL, respectively). Serum concentrations of E-2 after implantation of the steroid did not differ fi om those present while rams were intact (P > .10) . Testicular venous and arterial serum concentrations of OT were low and di d not differ within or between rams. These results suggest that restoration of E-2 concentrations to physiological levels in castrated adult rams (reg ardless of sexual orientation) cannot stimulate or reestablish sexual behav iors to levels observed prior to castration.