Case Report: Suppression of Harem Stallion Behavior and Fertility Following Anti-Gonadotropin-Releasing Hormone Vaccination of a Captive Wild Przewalski’s Horse (Equus ferus przewalskii).

This research aims to find a less invasive method for managing the reproduction of wild Przewalski’s horses, specifically stallions, with the use of anti-gonadotropin-releasing hormone (GnRH) vaccination.

Methodology

• The researchers performed non-surgical castration on a captive wild Przewalski’s stallion by administering an injection under the skin. This injection consisted of two doses of 450 μg (3 ml) of GnRH combined with diphtheria toxin, which was repeated every six months.
• Semen quality was evaluated by obtaining it through electro-ejaculation while the horse was under general anesthesia. The method proved to be safe and efficient.
• Movement of the obtained spermatozoa was initially poor but improved by diluting the sample after collection. Sample dilution ratios ranged from 1/4 to 1/5.
• Effects on the endocrine system and behavior were monitored over a two-year period following the treatment.

Results

• One month post-vaccination, the total spermatozoa number and movement decreased, although it did not confirm infertility at this stage.
• Six months after vaccination, the serum testosterone levels decreased, and the stallion lost its dominant role within the group. No motile spermatozoa were present, and no offspring were observed.
• At this point, the previously dominant stallion was no longer able to breed effectively, indicating that the vaccination had successfully suppressed its reproductive capabilities.

Conclusion

• The procedure of electro-ejaculation under anesthesia was determined as a safe and effective method to obtain spermatozoa in wild horses. Samples should ideally be washed or significantly diluted before being used for artificial insemination programs.
• The anti-GnRH vaccination resulted in a significant reduction in spermatozoa count and movement and a decline in testosterone production.
• Changes in the social structure of the group were noticed, such as the treated stallion, losing its dominant status.
• This technique could be considered a viable alternative to surgical castration in wild horses as it is less invasive and seems to effectively control their reproduction.