Testosterone-induced precocious sexual behavior in chickens differing in adult mating frequency

Precocious adult sexual behavior was determined for chicks from two lines of chickens selected bidirectionally for adult mating frequency. Three-day-old chicks were injected with either 0 or 12.5 mg testosterone cypionate (TC) in sesame oil, and their sexual responses to a hand thrust test (HTT) measured at 10, 12, 14, 16 and 18 days of age. TC stimulated copulation in both the high and low mating line, while birds receiving injections of the vehicle only, failed to copulate. There were differences in precocious sexual behavior between lines at this young age, although further differential maturation of neural tissues mediating mating behavior may occur. Courts, mounts, treads and matings were determined for these same birds at 7 weeks of age, following treatment with 25 mg TC. Differences were found between the lines, with high mating line birds scoring higher than low mating line birds for all behaviors measured. Early treatment with TC, however, had no direct effect on sexual behaviors at this age. Correlations between 7-week behaviors and HTT scores were determined and their possible meanings discussed.