Effects of GnRH immunization in sexually mature pony stallions.

The research article explores the use of Gonadotrophin releasing hormone (GnRH) immunization as an alternative to surgical castration in sexually mature pony stallions. The study shows promising results, where treatment not only induced strong antibody responses against GnRH but also led to decreased testosterone levels and impacted sperm motility and testis function.

Methodology

• The researchers tested two non-mineral oil adjuvant GnRH vaccines for their capability to prompt high antibody titers against GnRH and observed their subsequent effects on the stallions’ reproductive characteristics.
• The study included twelve sexually mature male hemicastrated Shetland ponies which were divided into three groups. The first two groups were given a specific dose of peptide equivalent of G6k-GnRH-tandem-dimer conjugated to ovalbumin (a protein found in egg white) in two different adjuvants – CoVaccine HT and Carbopol. The third group was given only the CoVaccine HT adjuvant as the control group.

Results and Findings

• The researchers didn’t observe any adverse effects in relation to injection sites or general health after immunization.
• Within two weeks of the second vaccination, all animals in the GnRH/CoVaccine group showed rapidly increased antibody titers against GnRH – this in turn, led to drastic reduction of testosterone levels sustained throughout the experiment.
• In contrast, the GnRH/Carbopol group showed intermediate antibody responses and effects on testosterone levels.
• Following the second immunization, sperm motility was negatively impacted in all stallions treated with the GnRH/CoVaccine and one stallion treated with the GnRH/Carbopol.
• Seven weeks post-second immunization, suppressed libido made semen collection impossible for one stallion from each group.

Conclusion

• Fifteen weeks after the initial immunization, histological examination of the testes showed reduction in seminiferous tubuli diameters (channels where sperm produced) in all stallions immunized with GnRH/CoVaccine and one from the GnRH/Carbopol group.
• This revealed extreme disorganization in spermatogenesis (the process of sperm cell development), as evidenced by lack of lumen in the seminiferous tubules, absence of spermatozoa and spermatids in tubular cross-sections, and inability to identify the stage of the tubular cross-sections.
• Testis size was also substantially reduced in three out of four stallions treated with GnRH/CoVaccine.
• The research concludes that two immunizations with G6k-GnRH-tandem-dimer-OVA conjugate in a suitable adjuvant, such as CoVaccine HT, can cause a rapid and complete reduction in serum testosterone levels in sexually mature stallions, leading to diminished sperm motility and affected testis function, with no adverse reactions observed post-immunizations.