Active immunization with a novel recombinant GnRH vaccine inhibits reproductive function in male goats

Gonadotropin-releasing hormone (GnRH) vaccines have been widely used to effectively inhibit gonadal development and reproductive function. To improve the immunogenicity of GnRH, we developed and evaluated the effects of GnRH6-kisspeptin-CRM197 immunization on the reproductive function in male goats. Thirty 3-month-old male goats (n = 30) were randomly assigned to control, surgical, and immunized groups. The immunized group received a 2 mL injection of the GnRH6-kisspeptin-CRM197 with a booster administered four weeks later. The control group was administered a white oil adjuvant. Blood samples were collected at regular intervals, and at week 20, the animals were euthanized for tissue collection. Serum antibody titers and testosterone levels were measured using ELISA and CLIA, respectively. Testicular parameters and histology were evaluated. The mRNA levels of reproductive-related genes in the HPG axis were measured using RT-qPCR. The results showed that the immunized goats had significantly increased serum GnRH and kisspeptin antibodies (P < 0.05) but decreased testosterone concentrations (P < 0.05) compared to the control group. Testicular size and histology were significantly affected in the immunized group, with notable reductions in testicular weight and dimensions (P < 0.01), and evidence of vacuolar degeneration and suppressed sperm production. The mRNA levels of FSHβ and LHβ in the pituitary, as well as FSHR, LHR, 3βHSD, and 17βHSD in the testis, were significantly lower in the immunized group compared to controls (P < 0.05). These findings suggest that GnRH6-kisspeptin-CRM197 is a safe antigen and a promising immunocastration vaccine with enhanced efficacy.