Re-stimulation of testicular function in GnRH-vaccinated stallions by daily GnRH agonist treatment.

This research investigates the effects of a Gonadotropin-Releasing Hormone (GnRH) agonist treatment on Shetland stallions that had been previously vaccinated against GnRH. The results show this therapy can help to restore testicular function in these animals.

Research Methodology

• Roughly, the study was conducted on twelve Shetland stallions, split into two equal groups: an experimental group and a control group.
• Within the experimental group, two doses of GnRH vaccine were given with an interval of four weeks.
• Samples of ejaculate and blood were gathered for studying semen features, testosterone concentration, and the levels of GnRH antibodies.
• Every horse in the experimental group underwent hemi-castration, where one testis was removed, when their testosterone levels dropped under 0.3 ng/mL. An age-matched control horse was treated the same.
• Post three weeks of hemi-castration, buserelin (a GnRH agonist) therapy was started at a rate of 4 μg/day for 4 weeks, and then ramping up to 8 μg/day.
• The remaining testicle was removed when testosterone levels in vaccinated stallions went beyond 0.5 ng/mL.

Key Findings

• GnRH vaccination led to an increase in the time a vaccinated stallion took to mount a mare, but buserelin treatment was found to decrease this time.
• The vaccinated stallions saw a reduction in total sperm count post-vaccination. This only saw a slight increase once buserelin therapy was started.
• Vaccination caused a drop in sperm motility and the proportion of membrane-intact spermatozoa (healthy sperm). The buserelin treatment, however, reversed these effects, restoring conditions to their pre-vaccination state.
• After vaccination, there was a decrease in testosterone concentration and testis volume. Buserelin treatment initiated a rise in both of these metrics.

Conclusion

The study concludes that while GnRH vaccination decreases testicular function, this effect can be reversed with a course of buserelin treatment. The researchers suggest this approach might be useful for stallions where testicular function has been long-suppressed due to GnRH vaccination. This provides an opportunity for temporary reversal of the impacts of GnRH vaccination, particularly in stallions that are temporarily not being used for breeding.