Effects of Porcine Zona Pellucida Immunocontraception on Mare Body Condition and Foaling Season Length in Two Western Wild Horse Populations.
Authors: Rutberg Allen T, Grams Kayla A
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Porcine Zona Pellucida Immunocontraception in Wild Horse Populations Wildlife managers increasingly employ immunocontraceptive vaccines to control wild horse populations, yet concerns persist about potential adverse effects on treated mares and their offspring. Rutberg and Grams examined two formulations of porcine zona pellucida (PZP) vaccine—ZonaStat-H (a simple emulsion) and PZP-22 (which includes a controlled-release component)—across two western US herds over six to seven years, measuring mare body condition scores, foaling season timing, and foal survival rates in treated versus untreated animals. Whilst PZP-treated mares experienced delayed and prolonged foaling seasons compared to controls, the vaccine produced no detrimental effects on maternal body condition beyond what would be expected from carrying a foal; moreover, foal mortality rates remained low and statistically equivalent between offspring of treated and untreated mares across both study populations. These findings suggest that the reproductive changes induced by PZP immunocontraception do not compromise mare welfare or foal survival, addressing a significant concern for practitioners and managers considering fertility control as part of evidence-based population management strategies. The results provide reassurance that PZP vaccination can be deployed as a humane population-management tool without secondary welfare consequences for breeding females or their progeny.
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Practical Takeaways
- •PZP immunocontraception can be safely used for population management in wild horse herds without causing secondary health effects in treated mares
- •Reproductive timing changes from PZP treatment do not compromise foal survival or development through their second year
- •Mare body condition management should focus on lactation demands rather than contraceptive method choice when implementing population control programs
Key Findings
- •PZP-22 vaccinations and boosters did not affect mare body condition scores beyond their contraceptive effects in either population (p > 0.05)
- •PZP-treated mares showed delayed and prolonged foaling seasons compared to untreated mares, but this did not harm foals
- •Foal mortality rates through age 2 years were low and virtually identical between foals of PZP-treated and untreated mothers (CM n=775, SWB n=640)
- •Summer body condition improved faster in mares without foals than mares with foals in both populations (p < 0.001)