My research explores changes in the social and sexual behaviour of feral horses that may be correlated with the application of the immunocontraceptive vaccine Porcine Zona Pellucida (PZP).
It has been suggested that PZP-treatment of mares in a population increases the rate of aggressive behaviours performed by the stallions. Because PZP works by inhibiting fertility, but does not prevent females from continuing to cycle throughout the season, a stallion with treated mares will have threats to his family throughout the breeding season. If he was able to successfully impregnate his mares these threats would be less as the mares would no longer cycle and would not attract as much attention from rival males.
In this photo, Galaxy makes amends with Prospera. Prospera's nerves are indicated in her tense posture and by the fact that the whites of her eyes are showing. She is also "clacking" her teeth, a submissive behaviour performed by young horses. Galaxy has developed a reputation for aggression, and is commonly seen disciplining his mares . Galaxy has a large harem, many of which have been treated with PZP, and is constantly driving them from location to location.
