The development of a safe and cost-effective non-surgical contraceptive that can be given orally as a vaccine and easily delivered to multiple cats would be a very useful tool for controlling stray and feral cat populations. Recent studies have shown that immunizing one animal species with proteins surrounding the female egg (zona pellucida, ZP) from another animal species stimulates an immune response in the recipient and blocks subsequent reproduction, presumably by preventing the male sperm from binding to the female egg. Studies in Germany have shown that antibodies against rabbit ZP are capable of blocking sperm from fertilizing the egg in cats. Together, this suggests that it should be possible to use rabbit ZP in a contraceptive vaccine for cats. If successful, this feline specific virus will be tested for its ability to induce contraception in cats and to vaccinate feral cats without worrying about antifertility effects on non-feline animal species living in the same areas.