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Animal Contraception

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Stephen L. Zawistowski, Ph.D.

Closing in on Contraception

Two years ago, I wrote a column about the dream of a simple pill or vaccine that could be given to dogs and cats to prevent unwanted pregnancies [see "The Magic Pill," p. 15, Animal Watch, Winter 2000]. Last April, I attended a conference on the status of nonsurgical methods of sterilization for animal population control. This meeting would be the chance to hear about the progress made toward the fulfillment of this dream. What I learned was both fascinating and sobering.

At the conference it was noted that the current "gold standard" for sterilization is surgical neutering, which provides contraceptive control as well as important ancillary benefits for animals, caretakers and veterinarians. For example, the surgically altered dog or cat shows reduced risk for a variety of medical conditions; the animal's caretaker no longer has to cope with behavioral changes associated with heat cycles; and the veterinarian builds a clientele, since most caretakers continue to take their animal companions to the same practice that performed the surgery. Another important benefit, at least in terms of population control, is that the procedure is a one-time event that provides permanent results.

Alternatives to Surgery
Ideally, future methods of contraception would provide all of these benefits without the labor, risk, cost or complications associated with surgery. So far, the immunocontraceptive techniques being used effectively on horses and a variety of wildlife species haven't been effective for cats. The formula, which uses extracts from the egg cells of pigs, doesn't induce the same broad immunological response that would result in sterility in cats as it does in other species. Further research is needed to identify an antigenic formulation that stimulates infertility in cats. It's important to note that even if successful, this method may not produce permanent sterility. Experience with wildlife has shown that the contraceptive effect is transient. This is not undesirable in terms of wildlife contraception, since maintaining a healthy population requires some breeding. It does, however, deviate from the desired gold standard for pet overpopulation.

In addition to immunocontraceptive techniques, time-released sub-cutical implants that block the hormones that regulate fertility have also been tested. The results so far have been promising, with induced infertility lasting as long as two years in dogs. Once again, while it's disappointing that the method does not produce permanent sterility, these methods may provide some relief in population control. Shelters and rescue groups that don't have the facilities to perform surgery may be able to produce short-term sterilization, at least until a new adopter can make arrangements with a veterinarian for spay or neuter surgery.

What Now?
The methods discussed at the conference are still mostly in the research and development stages. Some may work in theory, but their long-term effects on the animals that are treated with them are still unknown. Going back to our gold standard, any new methods must have no deleterious impact on the health of animals that receive the treatment. Other considerations are the broader ecological impacts that these contraceptives might have. Some conference attendees expressed concern about the effect of a product on predators who might kill and eat feral cats who are treated for population control. Does the product "bioaccumulate" in the food chain, and could it have a harmful effect on populations of wildlife? Finally, any product that produces infertility in dogs and cats might also be assumed to have a similar effect on humans. What safety measures will be needed to prevent either accidental or intentional misuse?

As it stands now, we're probably five years away from a product with broad application for animal fertility control. Development and testing of this "dream" product will probably cost $10 million or more. Several companies have already indicated that they are going to pursue this work, but humane groups may need to provide both moral and financial support for these efforts. In the meantime, however, the message to spay and neuter pets must be perpetuated - at least until we achieve a new gold standard.

Dr. "Z" is senior vice president of ASPCA Animal Sciences and Animal Watch science advisor.

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