A major goal in managing free-roaming cat populations has been to develop a safe and effective non-surgical contraceptive for cats. Research efforts have been ongoing for a number of years to achieve this global goal.
This study’s objectives were to measure the duration of contraception after a single intramuscular injection of a gonadotropin-releasing hormone-based vaccine (GonaCon) and evaluate its safe use in female cats living in cat colonies.
A previous formulation of the GnRH vaccine was evaluated in a 5-year breeding trial in 15 adult queens. In the earlier study starting 120 days post-vaccination, vaccinated cats had a significantly longer median time to contraception (39.7 months) compared to sham control treated cats (4.4 months). One side effect noticed from the study was of granulomatous injection-site masses appearing within 2 years in 33% (n=5/15) of vaccinated cats.
Subsequently, due to changes in the vaccine formulation plus consideration for potential injection site reactions, a short-term safety study was conducted using the current formulation of GonaCon in six adult spayed female cats. While transient injection-site reactions were noted in 66% of this group of cats, the levels of safety and immunogenicity were considered adequate for further evaluation.
In this study, Gonacon was administered intramuscularly (0.5 ml/cat) to 20 intact female cats, and saline was administered to 10 intact female cats as controls. Beginning 4 months after injection, all the cats were housed with fertile male cats in an environment that closely resembled a free-roaming colony cat population. Within 4 months of introduction of the male cats, all the control female cats (n=10/10) and 60% (n=12/20) of the vaccinated cats became pregnant. An additional two vaccinated cats became pregnant within one year of treatment. Litter size was significantly smaller in the GonaCon vaccinated group over the control group. There was a longer median time to conception following vaccination (212 days) compared to control group cats (127.5 days). Injection site reactions (transient swelling to granulomatous masses) were observed in 45% of vaccinated cats.
The authors state the results from the study were not anticipated. Two reasons for the difference of results with prior studies mention the potential of variability in the vaccine or individual response to the vaccine. They indicate that the level of contraception induced by the GonaCon dose and vaccine lot was not sufficiently effective to use under free-roaming cat conditions. Additional research continues to be conducted for the important goal of population management of cats. (VLT)
Vansandt LM, Kutzler MA, Fischer AE, et al. Safety and effectiveness of a single and repeat intramuscular injection of a GnRH vaccine (GonaCon™) in adult female domestic cats. Reprod Domest Anim. 2017 Apr;52 Suppl 2:348-353.