Veterinarian Dr. Judy Levy from the University of Florida has put immunology to work in testing out what could be a breakthrough in controlling the feral cat population. Her group tested out the contraceptive vaccine GonaCon on laboratory cats (which were subsequently all adopted). GonaCon works by stimulating production of antibodies to GnRH, a hormone that in turn signals the production of sex hormones, including those involved in sexual behavior and ovulation. By binding to GnRH, the antibodies induced by the vaccine interfere with GnRH's activity, preventing the release of these sex hormones. This inhibits sexual activity and the animals will remain nonreproductive as long as sufficient GnRH antibody levels are present.
The vaccinated cats all responded to the vaccine with varying levels of success, but overall the trial was a success. Dr. Levy found that the vaccine (which was originally formulated for use on deer, but also works on other mammals) was safe and long-lasting after just one dose.
Vaccinated cats had a longer time to conception (median 39.7 mo) compared to sham-treated cats (4.4 mo; P < 0.001). A total of 93% of vaccinated cats remained infertile for the first year following vaccination, whereas 73, 53, and 40% were infertile for 2, 3, and 4 y, respectively. At study termination (5 y after a single GnRH vaccine was administered), four cats (27%) remained infertile. (Journal of Theriogenology – login required for full article)
Not a bad turn out. This seems like a promising method of contraception for feral cats. Granted, it doesn't have extremely long-lasting effects in all cats, but still, if it makes a female miss even a few breeding cycles, that can be a few litters of feral cats prevented. GonaCon is also evidently fairly cheap, so it is a cost-effective method of sterilization compared to spaying.