Porcine zona pellucida (PZP) contraceptive vaccines offer a humane alternative to roundups and euthanasia for managing feral horse populations and controlling reproduction in sanctuary settings.
PZP contraception represents a welfare-superior approach to feral and sanctuary horse population management. Traditional population management has relied on roundups — helicopter-driven captures causing significant stress and injury — followed by either holding in facilities or fertility surgery. Both approaches have substantial welfare costs. PZP darting, by contrast, requires only that horses be approached close enough for a dart gun shot — stressful briefly but without the extended capture trauma of roundups. The contraceptive effect is reversible when management goals change, unlike surgical sterilization. For sanctuary populations, PZP prevents unwanted breeding while allowing horses to express normal reproductive behavior. The evidence from long-term programs like Assateague Island demonstrates that PZP-managed populations can be stable, healthy, and behaviorally normal over multi-decade periods.