Histological Findings in Testes of Baboons ( Papio spp.) and Dwarf Bucks ( Capra hircus ) Subject to Repeated Immunisation Against GnRH

BACKGROUND: Immunocontraception is a population management strategy based on vaccines that induce an immune response against reproductive targets such as GnRH. OBJECTIVES: This study aimed to investigate spermatogenic activity in adult baboons and adult dwarf bucks subject to repeated immunisation against GnRH for extended periods. METHODS: In Experiment 1, histological findings in untreated dwarf bucks (CONTROL-1) (n = 10) were compared with those found in males repeatedly immunised against GnRH (Improvac) during 5 years (RI-1; n = 15). In Experiment 2, one group of baboons received immunocontraceptive treatment against GnRH during 5-10 years until death (RI‑2; n = 6). The second group received the same treatment for 10 years before discontinuation, with the interval between treatment withdrawal and death ranging from 10 to 27 months (RI‑2+S; n = 19). As in Experiment 1, testicular tissue was collected post-mortem and processed histologically. RESULTS: In both species, the testicular tissue of animals treated with repeated immunisation against GnRH showed an absence of active spermatogenesis. The mean seminiferous tubule diameter in bucks was smaller in the RI-1 group than in the CONTROL-1 group (108.69 ± 13.17 µm vs. 187.35 ± 14.38 µm; p < 0.05). In baboons, morphometric analysis showed similar seminiferous tubule diameters in the RI-2 (82.63 ± 4.47 µm) and RI-2+S (79.23 ± 5.89 µm) groups. CONCLUSIONS: In bucks and in more than 70% of baboons, the severity of degenerative changes in the germinal epithelium suggests that long-term repeated immunisation against GnRH may lead to irreversible infertility.