The study analyzes the use of Porcine Zona Pellucida (pZP) as a contraceptive in free-roaming wild horses in Nevada’s Virginia Range, showing that over four years, treatment resulted in a 58% reduction in foaling and gained 70% population coverage.

Research Objectives and Methodology

• The study was conducted on the free-roaming wild horse population of Nevada’s Virginia Range.
• One of the main objectives of the study was to investigate the efficacy of immunocontraception method using porcine zona pellucida (pZP) in managing the reproductive rate of these horses.
• The pZP contraceptive treatment was delivered to mares via remote darting, a non-invasive method that does not require capturing or restraining the animals.
• The effects of the treatment on annual birth rates and population demographics were examined, and the frequency of treatment was evaluated in relation to these variables.
• Researchers recorded the monthly data of mares over a period of 48 months, from January 2019 to December 2022, to track changes in vaccination numbers, chances of pregnancy and conception, and demographic composition based on age.

Key Findings

• The data showed a noticeable decrease in the foaling rate, indicating the contraceptive treatment was effective in controlling the population growth of the horses.
• There was also a significant drop in the numbers of mature mares, leading to a decrease in the annual seasonal breeding peaks. However, the foaling season duration didn’t change.
• After four years, the population coverage of the pZP treatment went beyond 70% of the overall horse population, resulting in a 58% reduction in foaling.
• Furthermore, the conception rate decreased to 10%, suggesting a significant decline in fertility among the treated mares.

Implications of the Findings

• Within the examined period, the ratio of vaccinated mares showed a steady increase.
• The system indicated stability with an average of about one vaccination per mare per year, assuming a 12-month efficacy decay rate for the contraceptive.
• These results provide practical insights for designing and implementing humane and effective fertility control programs, contributing to best management practices for wild, free-roaming horse populations in regions facing development-related constraints.