Bisexuality in the prepubertal male pig

Intact and castrated male pigs were given weekly tests between the ages of 3 and 5.5 months with either an adult male or an adult oestrous female partner. All intact male subjects mounted, and mounting occurred an early as 3 months of age. When mounted by males, 86% of the intact males displayed the female receptive posture (immobilization) at least once, and average receptivity scores were high. Thus prepubertal male pigs are behaviourally bisexual. Both mounting and immobilization were much less frequent in the castrated males; their occurrence in intact males is due to testicular hormones. In the intact males, receptivity did not decrease during the 30 week testing period, in contrast to evidence from previous studies, using adult tests, for progressive defeminization during the prepubertal period.