One-year reproductive effects of anti-GnRH and rabies vaccination in female pet cats

Abstract Overpopulation of domestic cats poses risks to public health, biodiversity, and animal welfare. Surgical sterilization is broadly used, but has substantial limitations. Gonacon, an anti-GnRH vaccine, provides a non-surgical alternative; however, data are lacking for owned queens in natural habitats and for simultaneous vaccination against rabies. We evaluated the one-year immunogenicity, safety, and efficacy of simultaneous Gonacon-rabies vaccination in pet queens and compared responses between indoor and outdoor cats. In a prospective field study, 36 intact queens (≥6 months) received Gonacon-rabies vaccination (Gonacon-Rabies, n=30) or ovariohysterectomy with rabies vaccination (Ovx-Rabies, n=6). Queens remained under owner care and were monitored at 0,3,6, and 12 months. Twenty-five queens completed follow-up (22 Gonacon-Rabies, 3 Ovx-Rabies). Injection-site nodules were observed only following Gonacon vaccination (13.6% vs. 0%;P=0.0564). Anti-GnRH seropositivity was detected in 68.2%,31.8%, and 27.3% of Gonacon-Rabies queens at 3,6, and 12 months, respectively. Among responders (n=15), 53.3% were positive only at 3 months, 6.7% up to 6 months, and 40% throughout. Gonacon-vaccinated non-responders were all outdoor queens (Outdoor: 7/13;53.8%; Indoor: 0/9; P=0.0167). Duration of anti-GnRH immunity was shorter in outdoor queens (2.1±0.9 vs. 8.3±1.5 months;P=0.0005). Reproductive events (estrus/pregnancy) occurred in 76.9% of outdoor vs. 11.1% of indoor Gonacon-Rabies queens (P=0.0075). AMH concentrations were inversely correlated with anti-GnRH levels (r=−0.53;P<0.0001). Rabies antibodies remained protective (≥0.5IU/mL) but were lower in outdoor vs. indoor queens (P=0.0490). Owner satisfaction was higher for Gonacon-Rabies indoor queens and those without reproductive events. Simultaneous Gonacon-rabies vaccination was safe and partially effective over one year, with better responsiveness in indoor queens. Lay Summary Domestic cats are highly prolific, contributing to overpopulation that negatively affects animal welfare, wildlife biodiversity, and public health. Although surgical sterilization is widely used to prevent cat reproduction, it has important practical, economic, and ethical limitations. We studied the safety, immune response, and reproductive effects of a contraceptive anti-GnRH vaccine (Gonacon), administered concurrently with a rabies vaccine, in female pet cats living under normal home conditions. The combined vaccination was generally safe, and most queens maintained protective immunity against rabies. However, the contraceptive effects varied considerably among animals. Indoor queens developed stronger, longer-lasting immune responses and experienced fewer signs of heat and fewer pregnancies than outdoor queens. In contrast, many outdoor queens showed weaker and shorter-lasting immune responses. These findings suggest that the combined vaccination may provide a practical non-surgical approach to controlling reproduction in some pet cats, but that living conditions can strongly influence its effectiveness.