Dose-dependent effects of a recombinant GnRH vaccine on reproductive function and growth performance in male goats.

Objective This study aimed to develop a recombinant gonadotropin-releasing hormone (GnRH) vaccine and to investigate the effects of different immunization doses on immunocastration efficacy and growth performance in male goats, providing an animal welfare-friendly alternative to surgical castration. Methods Forty male goats were randomly assigned to four groups (n = 10 per group): the saline-injected control (NC), surgical castration (SC), low-dose vaccine (LD), and high-dose vaccine (HD). The vaccine was administered according to a scheduled immunization program. Anti-GnRH antibody titers, serum testosterone concentrations, libido scores, histological characteristics of testicular tissues, and growth performance were evaluated to assess immunocastration efficacy. Results Both LD and HD groups exhibited significantly higher anti-GnRH antibody titers than the NC group (p < 0.01). Serum testosterone concentrations and libido scores were markedly reduced in the immunized groups (p < 0.01), indicating effective suppression of reproductive function. Histological and quantitative analyses demonstrated pronounced testicular atrophy in immunocastrated goats, characterized by a significant reduction in seminiferous tubule diameter and spermatogenic cell number, as well as the absence of spermatozoa within the lumen. Although only limited time points showed significant differences between the two immunization doses, the overall immunocastration efficacy of the low- and high-dose regimens was largely comparable, with the low-dose group exhibiting slightly stronger suppression at certain parameters or time points. Additionally, immunocastrated goats had significantly higher body weight and weight gain compared with surgically castrated goats (p < 0.01), while differences with the NC group were not significant (p > 0.05). Conclusion The recombinant GnRH vaccine effectively suppresses reproductive function in male goats. Compared with surgical castration, immunocastration was associated with improved growth performance, while no significant differences were observed relative to intact animals. These findings support immunocastration as a non-invasive and welfare-friendly alternative to surgical castration in livestock production.