Aim: The aim of the study was to investigate the histological appearance of testis, epididymis, prostate and seminal vesicles of ram lambs immunized against gonadotrophin releasing hormone (GnRH). Methods: The study was performed on 14 male lambs, 7 in the study group and the other 7 in the control group. Another 5 lambs were included from the study after biopsy samples were taken from their testes at age 10 weeks to determine testicular histology at the start of the study. Seven male lambs aged 10 weeks were immunized against GnRH using a recombinant GnRH fusion protein vaccine. The immunization was repeated twice monthly until slaughter at 9 months of age. Testes and epididymis biopsies were taken at the 6th month. After slaughter, testis, epididymis, prostate and seminal vesicles were extracted for histopathological investigation. Results: At the 6th month and at slaughter histopathology of all the sex glands, most evidently in the testes, indicated secondary infertility. In the study group, tubule diameter decreased and spermatogenetic activity disappeared. The ball of sperm cells seen in the epididymis tubules of the control group at the 9th month was not seen in the study group. Changes in prostate tissues between the study and control groups were not evident but stromal tissue in the seminal vesicles increased in the study group. Conclusion: In conclusion, the histomorphological changes showed that recombinant GnRH fusion proteins provided immune castration in male lambs when used at an early age.