Prolonged reproductive suppression in domestic cats following a booster dose of an anti-GnRH vaccine.

Immunocontraception via anti-GnRH vaccination offers a non-surgical alternative for managing reproduction in domestic cats, but data on the long-term efficacy of booster protocols remain limited. The study aims to evaluate the efficacy and safety of administering a booster dose of an anti-GnRH vaccine Improvac™ 300 days after primary immunization to prolong reproductive suppression in domestic cats. Twenty-one adult female cats and seven adult male cats received a primary two-dose series of the anti-GnRH vaccine 30 days apart, followed by a booster dose at day 300. Animals were monitored for 540 to 720 days post-booster. Assessments included physical and ultrasonographic examinations, reproductive behavior, vaginal cytology, testicular volume, penile spine characteristics, reproductive hormone concentrations, and hematological parameters. All animals respond to the treatment. In male cats, the booster dose accelerated reduction in testosterone, testicular volume, and penile spine size compared with primary immunization alone. Reproductive suppression was extended for 420 days in two queens, 450 days in five queens, 690 days in four queens, and 720 days in ten queens. Serum progesterone remained basal, and no pregnancies were recorded. Some animals (n = 22) showed transient loss of appetite, but hematological parameters remained within reference ranges, and no injection-site inflammation or tenderness was detected. Administering a booster dose 300 days post-primary immunization safely and effectively prolongs immunocontraception in both male and female domestic cats, providing a viable long-term alternative to surgical sterilization.