Bisexuality in the prepubertal male pig

Area of Science:

• Animal behavior
• Endocrinology
• Reproductive biology

Background:

• Prepubertal sexual behavior in male pigs is not well understood.
• Previous studies suggested defeminization occurs during the prepubertal period.

Purpose of the Study:

• To investigate the sexual behavior of intact and castrated male pigs during the prepubertal period.
• To determine the role of testicular hormones in male pig sexual behavior.

Main Methods:

• Weekly behavioral tests were conducted on intact and castrated male pigs from 3 to 5.5 months of age.
• Subjects were paired with adult male or estrous female partners.
• Mounting behavior and female receptive posture (immobilization) were recorded.

Main Results:

• All intact male pigs mounted partners, with mounting observed as early as 3 months.
• 86% of intact males displayed immobilization when mounted by males, indicating bisexual behavior.
• Mounting and immobilization were significantly less frequent in castrated males.
• Receptivity in intact males remained high throughout the 30-week testing period, contradicting previous findings.

Conclusions:

• Prepubertal male pigs are behaviorally bisexual.
• Testicular hormones are crucial for mounting and receptive behaviors in male pigs.
• Unlike previous evidence, prepubertal male pigs do not appear to undergo progressive defeminization during this developmental stage.