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Sterilization Drugs for Cats

Not a Substitute for Surgical Spaying in Owned Cats


An Even Better Solution is in Sight

Animal advocates breathlessly await the announcement of a new sterilization drug, which could be administered by injection, pill, or even as a food additive. The latter, depending on cost, would be a boon to managers of feral cat colonies who struggle daily to trap wily ferals. Many feral colony managers include vaccinations in their trips to the vet, but spay/neuter procedures are the "biggie," cost-wise, besides requiring invasive surgery in a controlled environment. Sterilization drugs are being developed on several frontiers:

  • Virginia-Maryland Regional College of Veterinary Medicine Project
    In 1998, student Michelle Meister-Weisbarth, in conjunction with Dr. Stephen Boyle, developed a genetically engineered bacterium (Salmonella), which when fed to female cats, would prevent eggs from fertilization.

    "Meister-Weisbarth then introduced a gene encoding a protein derived from the zona pellucida surrounding the vertebrate egg into the salmonella. The bacterial vaccine is capable of inducing the production of antibodies which recognize the zona pellucida and block the ability of a sperm to fertilize the egg."
    CNN Article Current plans involve testing by scattering of the vaccine-laced food pellets in areas populated by feral cat colonies. Of major importance will be the study of what effect, if any, the medication will have on the psychology of the colonies. Meister-Weisbarth says it may be two to five years before the drug will be available for public use, as the FDA will want proof there is no negative impact on the environment.

  • Injectable Vaccine from University of Georgia Vet
    Dr. Richard Fayrer-Hosken, a veterinarian at the University of Georgia, has developed a drug, based on similar research, which is injectable. Fayrer-Hosken wants to test it on at least a thousand dogs before seeking approval from the FDA.

  • SpayVac - University of Florida
    The Winn Feline Foundation has given a $14,484 award to a team at the University of Florida for research in the "Nonsurgical alternative to altering feral cats: 'EVALUATION OF SPAYVAC(tm) FOR STERILIZING DOMESTIC CATS (FELIS CATUS).'" SpayVac has already been proven to reduce fertility in Barbery sheep, rabbits, and several seals species, and the U. of Florida team hopes to prove its effectiveness in sterilizing feral cats.

  • RU-486 as a Cat Sterilization Agent?
    Mibolerone, a close chemical relative of Mifepristone (an ingredient in RU-486), which is an androgen steroid which blocks the production of progesterone, which is needed to sustain pregnancy. For various political reasons, mibolerone has not been available for public use, and in its present form is not cost-effective for sterilization in a larger context. In fact, in 1985, after the FDA banned the importation of RU-486 into the U.S., the Carnation company quietly discontinued its previously announced plans to market a birth control dog food, tentively called "Extra Care."

    However, it is thought that in the present climate, if mibolerone could be manufactured in sufficient quantity, with appropriate formulations, it might again present a viable alternative to surgical spaying.

None of these immunocontraceptive vaccines are expected to be a substitute for surgical spaying of owned female cats. Why? Because they do not stop ovulation, nor the attendant frustrated behavior of female cats in heat. Furthermore, surgical spaying helps prevents ovarian cancer and mammary tumors.

Barring an unexpected announcement, it seems apparent that it will be at least another couple of years before any of these "contraceptive" drugs will be available While we wait impatiently for these drugs to reach the hands of those who need them another three to five million kittens will be born. At least, there is light at the end of the tunnel.

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