Preliminary study of ovarian activity in fillies treated with a GnRH vaccine.

The study researched if two varying doses of a gonadotrophin-releasing hormone vaccine impacted ovarian activity in 2-year-old fillies (young female horses). The research concluded that vaccination did suppress ovarian function and prevent oestrous behaviour, but these effects were reversible and did not affect the fillies’ fertility in the long term.

Research Design & Methodology

• The study randomly assigned six 2-year-old Australian Stock Horse fillies to one of three groups. One group remained unvaccinated as a control, while the other two groups received either a 200 mg or 400 mg dose of the gonadotrophin-releasing hormone (GnRH) vaccine.
• The chosen quantities of the vaccine were administered to the fillies using a controlled vaccination dose rate experiment. This research approach was employed to accurately determine how these specific doses of the vaccine would influence ovarian activity.

Results

• Results indicated that the GnRH vaccine suppressed ovarian activity at the peak of the breeding season in the treated fillies compared to the untreated controls. The effects were observed for 25 and 30 weeks in the 200 mg and 400 mg groups, respectively.
• The controls, on the other hand, showed regular oestrous activity and behaviour.
• Furthermore, the research found that the fillies’ ovarian activity ceased 2 to 3 weeks after receiving the primary vaccination, indicating that the GnRH vaccine had a fast-acting effect on the reproductive system of the fillies.
• The vaccine did not seem to affect plasma androstenedione concentrations, suggesting that it targeted specifically gonadotrophin-releasing hormones.
• The study also monitored the horses’ antibody levels. These levels were low until after the booster immunisation, after which they rapidly increased to much higher levels.

Conclusions

• The research concluded with the observation that the effect of the GnRH vaccination on the fillies was reversible. This was indicated by the return of normal ovarian function in the horses following suppression.
• Moreover, the fertility of the vaccinated fillies remained unaffected by the vaccine, as evidenced by the fact that they were able to conceive normally in the subsequent breeding seasons.