Suppression of behavioural and physiological oestrus in the mare by vaccination against GnRH.

The study was about testing an equine immunocontraceptive vaccine made from Gonadotropin-Releasing Hormone (GnRH) for its ability to suppress estrous behavior in mares. In the trial, the vaccinated mares demonstrated reduced hormone levels and estrous behavior for a minimum of three months post vaccination.

Research Methodology

• The study involved a total of 24 mares located across two sites in Australia. All the mares were vaccinated with an immunocontraceptive vaccine that included GnRH coupled with a carrier protein and an immunostimulating complex acting as an adjuvant.
• As a control measure, twelve mares from each site were given only the adjuvant and their estrous, hormonal, and behavior patterns, as influenced by seasonal changes, acted as the baseline for the study.
• Aspects measured among all the mares included the reactions occurring at the injection sites, the ovarian and follicular activity, the levels of antibody in serum, the levels of 17beta-oestradiol and progesterone, and behavioral patterns following vaccination. Particularly, the mares were exposed to a stallion to observe and record any estrous behavior.

Findings

• All the vaccinated mares responded to the vaccination by showing a high antibody response towards GnRH. The peak response was observed after two weeks from the second vaccination which then slowly dropped over the following weeks.
• As the anti-GnRH antibody levels increased, the level of ovarian activity significantly decreased. This led to a substantial reduction in levels of 17beta-oestradiol and progesterone hormones among the 24 vaccinated mares.
• In response to the teaser stallion, a reduction in the estrous-related behavior was noted among the vaccinated mares. The mares maintained this reduced level for at least three months, with the length of this period directly correlated to the magnitude of the initial antibody response.

Conclusions

• After two doses of the vaccine, it proved effective at inhibiting estrous behavior among the mares for a minimum of three months.
• The vaccine demonstrated a high safety level as there were no significant local or systemic adverse reactions reported following the vaccination.
• This commercially available equine immunocontraceptive vaccine featuring GnRH could be a viable option for controlling estrous behavior in mares, which in turn reduces their fertility for a significant period, making it a possible method of population control.