Testicular control of defeminization in male pigs.

Female mating behavior, defined as expression of the immobilization response ("mating stance") in the presence of an intact male, was monitored in gonadectomized, hormone-treated female and male pigs to evaluate sexual dimorphism for this trait. When treated postpubertally with estradiol benzoate (EB), the relationship between dosage of EB and proportion of pigs that showed an immobilization response, as well as duration of this response, was similar in ovariectomized females and males castrated at 2 weeks of age (neonatally). Males castrated at 8 months of age (post-pubertally) showed little response to EB treatment. In males castrated at different ages from birth to 8 months, the proportion showing an immobilization response was less for males castrated at 6 months than observed in males castrated at birth or 2 months of age, and the duration of response to EB was shorter for males castrated at 4 months of age or later. When androgens were evaluated for their effectiveness, testosterone propionate (TP), at the dosages used, induced the immobilization response in all females and neonatally castrated males. Females did not show a response to dihydrotestosterone propionate treatment. An immobilization response was observed in some, but no all, postpubertally castrated males with high dosages of EB or TP; but the frequency of response did not increase with increasing dosage of TP greater than 250 micrograms/kg body weight. These observations indicate that female mating behavior in pigs is a sexually dimorphic trait and suggest that the sensitive period sexual differentiation of this trait in males is associated with increased testosterone secretion during pubertal development.