Porcine zona pellucida (PZP) immunocontraception of wild horses (Equus caballus) in Nevada: a 10 year study.

The research investigated the effectiveness of Porcine zona pellucida (PZP) immunocontraception in free-roaming wild horses in Nevada over 10 years. The study found that the PZP vaccine provides up to a 94% infertility rate in these horses, with fertility returning to normal within a year.

Research Method and Objectives

• The researchers studied the use of Porcine zona pellucida (PZP) immunocontraception for potential use in controlling the population of wild horses in Nevada, USA. The objective was to test the effectiveness of one- and two-year vaccine protocols and examine practical aspects of managing such a contraceptive program.

Vaccine Protocol

• Initially, a vaccine protocol of two injections (spaced 3-4 weeks apart), effective for a duration of 1 year, was used.
• This was followed by the development and field testing of a single-injection controlled-release vaccine also with a duration of 1 year.
• A presumptive vaccine designed to last for 2 years was later initiated.

Data Collection and Analysis

• The researchers monitored anti-PZP antibody titre response, conducted pregnancy testing, and tracked offspring production as part of the data collection process.
• The data revealed that the PZP vaccine could achieve infertility rates of up to 94% in free-roaming wild mares.
• The single-injection PZP vaccine, which included a controlled-release component of PZP in a polymer matrix, was found to have equivalent effectiveness to the two-injection vaccine, providing a high rate of infertility.
• All tested PZP vaccine preparations were associated with a return to normal fertility within 1 year.

Practical Application and Management

• The research also examined the practical aspects of managing a PZP contraception program. The vaccine was prepared in pellets that fitted into the needle of a dart or syringe, simplifying handling and facilitating long-term storage.
• A vaccine delivery method using a jabstick on captured mares trapped in a chute during routine gatherings was adopted. This added to the efficiency and safety of vaccine administration.
• The researchers developed a vaccine-training program to ensure personnel safety during vaccine preparation and administration, maximising overall safety of the program.