Assessing the feasibility of microneedle patches for GnRH immunocontraception in mixed-breed dogs (Canis familiaris)

The overpopulation of free-roaming dogs poses significant risks to endemic species, public health, and the environment through predation and disease transmission. While surgical castration is effective, it raises ethical concerns regarding animal welfare. Immuno-castration offers a humane and effective alternative for population control, but a more easily administered and cost-efficient method is needed to enable widespread vaccination efforts. In this study, we aimed to employ self-dissolving microneedle patches for a simple and potentially cost-effective immunization of a recombinant GnRH-based vaccine to control fertility. Eight mongrel dogs were randomly divided into 2 groups (n=4 each) and immunized with the recombinant GnRH-based vaccine through either intramuscular injection (IM group) or microneedle patches (MN group), respectively, as the primary immunization, followed by an intramuscular booster 4 weeks after. Production of GnRH-specific antibodies was detected 2 weeks after the primary immunization and lasted for at least 12 weeks. Moreover, the serum testosterone level was decreased in vaccinated males. Additionally, testicular atrophy and poor semen quality (concentration, abnormality, and viability) were found in all vaccinated dogs. Based on our results, the GnRH vaccine appeared to successfully elicit GnRH-specific antibody responses, which leads to reduced serum testosterone concentration, testicular atrophy, and poor semen quality in both IM+IM and MN+IM schemes. Self-dissolving microneedle patches may be a feasible approach to mass dog vaccination in the future.