January 15, 2007


 Getting beyond surgical contraception

Nonsurgical alternatives explored as possible answer to dog and cat overpopulation

Posted Jan. 1, 2007


Surgical sterilization has long been considered the gold standard for managing dog and cat populations in the United States. Yet the millions of stray and unwanted companion animals euthanized each year in this country raise questions about whether the gold standard is really just gold-plated, and if there's a better way of reducing the numbers of surplus animals.

The most obvious shortcoming of spaying and neutering as methods of population control is one of logistics. For a number of reasons, ranging from a lack of responsible pet ownership to affordability, too few cats and dogs are being sterilized. Early spaying and neutering, discounted surgeries, or mandatory sterilization requirements for pet adoption have all been offered as solutions to the overpopulation problem.

The sad reality remains, however. The number of new litters of fertile dogs and cats born each day in the United States vastly exceeds the delivery system for surgical sterilization, resulting in excess numbers of unwanted animals. Those not fortunate enough to be adopted can become victims of starvation, trauma, and disease.

Dr. Margaret Slater, an associate professor of epidemiology at Texas A&M University, recently highlighted the overpopulation problem as it applies to cats. Speaking this past November at an international symposium in Alexandria, Va., on nonsurgical contraceptive methods for population control, Dr. Slater explained that the number of feral and stray cats in the United States is estimated at around a third to a half that of the owned cat population, which translates into 30 to 45 million free-roaming cats.

More than a hundred people from across the world gathered at the symposium, hosted by the Alliance for Contraception in Cats & Dogs, to hear about the latest developments in dog and cat population management and new contraception technologies. While surgical sterilization is an essential tool in pet population control, ACC&D President Joyce Briggs believes additional contraception options are desperately needed.

"I believe that when we are still euthanizing millions of animals as a means of managing dog and cat populations, it's a crisis," Briggs said.

What the ACC&D is searching for is a drug, vaccine, or implant that is safe, inexpensive, and capable of rendering a cat or dog permanently sterile after a one-time procedure. Such a holy grail of chemical castration has yet to be discovered. But considering the scope of the surplus dog and cat problem, the alliance is stepping up its efforts to support research for the eventual development and commercialization, both domestically and abroad, of dog and cat contraceptives. The AVMA encourages research into the development and use of nonsurgical methods of sterilization.

Also presented during the symposium was an emerging body of research suggesting that surgical sterilization can cause some adverse effects, such as incontinence, vaginitis, and increased aggression in female dogs. Evidence suggesting that surgical sterilization might cause health and behavioral problems has not been studied in a systematic way by the veterinary profession.

Although the need for an effective chemical alternative to surgical sterilization is obvious, the focus and funding to develop such a product has been low. For the most part, the pharmaceutical industry has been reluctant to invest in bringing a dog or cat contraceptive to market because pet owners would likely not pay for something that isn't entirely safe, effective, or convenient, according to Dr. Wolfgang Jöchle, a diplomate of the American College of Theriogenologists, and one of the symposium speakers.

"The requirement for the replacement of spay and neuter has to be 100 percent perfect. Pharmaceutical companies would have to come up with a perfect drug," Dr. Jöchle said. He added that, while there are many "exciting possibilities" on the horizon, there isn't a single dog or cat contraceptive drug the pharmaceutical industry is immediately willing to invest in.

Currently, there is no commercially available contraceptive drug approved for dogs and cats in the United States. A zinc gluconate intratesticular injection for sterilizing male dogs went on the market in 2003. For business reasons that had nothing to do with the drug's safety and efficacy or with consumer demand, the manufacturer pulled the product from the market after just two years. Abbott Laboratories is expected to begin producing and selling the contraceptive in the near future.

Overseas, the situation regarding dog and cat contraceptives is much the same as in the United States, although the European Union recently approved a one-year reversible contraceptive implant for female dogs. Limited research has also revealed that the drug suppresses estrus in female cats for nearly three years, and additional research is being conducted.

Both here and abroad, the search for effective chemical contraceptives is under way. Loretta Mayer, PhD, has been treating female dogs with an industrial chemical that causes sterility in rodents by preventing development of ovarian follicles. At the symposium, Dr. Mayer, an assistant research professor at Northern Arizona University, presented this method, still in its early stages, as a possible means of achieving permanent sterilization. Dr. Mayer is working on doses and formulations for a single-injection application. She is also involved in preliminary studies at the University of Florida to test the drug's effectiveness in cats.

The usefulness of a chemical contraceptive can vary regionally, according to Dr. Julie Dinnage, executive director of the Association of Shelter Veterinarians. In parts of the Northeast, for example, stray dogs aren't a major problem like they are on some American Indian reservations and in developing countries. Elsewhere, it is large populations of feral cats that need to be controlled. A chemical alternative to spaying and neutering that targeted cats would, therefore, be of greater use than one aimed at dogs.

"We're going to need more than one option," Dr. Dinnage said. "I don't think it's going to be one silver bullet that's going to take care of the entire overpopulation problem. So the more tools we have to deal with issues in individual, very unique communities, the better poised we're going to be to really address this problem on a nationwide basis, and certainly internationally as well."