Recombinant GnRH6-kisspeptin-CRM197 vaccine inhibits reproductive function in male rats and dogs.

Immunocastration vaccines, as an alternative to surgical castration, have gained prominence for improving meat quality in livestock by suppressing reproductive functions. Central to this process is gonadotropin-releasing hormone (GnRH), a pivotal regulator of the hypothalamic-pituitary-gonadal axis whose secretion is modulated by the upstream neuropeptide kisspeptin. Building upon this regulatory hierarchy, we developed a novel GnRH6-kisspeptin-CRM197 conjugate vaccine targeting both signals simultaneously. This study systematically evaluated the vaccine's effects: First, by assessing its inhibitory impact on testicular development, reproduction-related gene level and hormonal secretion in thirty male rats through ELISA, RT-qPCR and histological analyses; Second, by conducting translational validation through preliminary field trials in ten male dogs to determine its practical efficacy for non-surgical castration. In male rats, the vaccine significantly increased anti-GnRH and anti-kisspeptin antibodies (P < 0.01), reduced serum testosterone levels (P < 0.01), decreased testicular size (P < 0.01), and suppressed spermatogenesis, with fewer germ cells across developmental stages. Hypothalamic GPR54 and GnRH mRNA and pituitary FSHβ, LHβ, and GnRHR mRNA levels were significantly reduced (P < 0.05). In male dogs, serum testosterone levels decreased by approximately 40-65 % in three immunized individuals, decreased slightly in two, and increased slightly in three. Four dogs showed complete absence of sperm, and four others showed markedly reduced sperm counts. These results indicate that the dual-target vaccine effectively suppresses reproductive function in rats and shows partial efficacy in dogs, supporting its potential as a non-surgical castration tool. Variability in canine responses highlights species-specific optimization needs.