New strategies, technologies are helping the overpopulation war

Q. What's new with spay/neuter programs?

A. Last month, Dr. Brenda Griffin gave a lecture on small animal spay/neuter programs at the 2005 American College of Veterinary Internal Medicine Forum in Baltimore. Some relevant points in this lecture are provided in this column.

For more than 30 years, researchers have been studying methods to control reproduction. Tremendous advances have been made in recent years with many successes in the human and wildlife fields. During this time, a few scientists have been working to apply these technologies to dogs and cats.

Contraceptive drugs and vaccines work by exerting a targeted pharmacological effect or prompting an immune response that inhibits or blocks some component of the animal's reproductive system, resulting in infertility. These products will greatly facilitate sterilization of dogs and cats because they will not require the commitments of technical expertise, equipment and time that surgical sterilization requires. The ideal contraceptive product would rapidly induce permanent sterilization, eliminate breeding behavior as well as fertility, and provide the same health benefits as surgical sterilization while requiring only a single dose. Furthermore, the ideal product would be effective in dogs and cats of both sexes and all ages, and be safe and easy to administer. At this time, no single product is able to fulfill all of these criteria.

New pharmaceutical agents include two products which have recently been released: Neutersol® (Addison Biologic, Mo.) and Suprelerin® (Peptech Limited, NSW, Australia). Neutersol is the first permanent, non-surgical method of sterilization for companion animals. It is currently licensed for use in the United States for chemical castration of puppies 3-10 months of age, although it has been shown to be effective in adult dogs and cats as well. It is an intratesticular injection of a zinc compound (zinc gluconate neutralized by arginine) that results in sclerosis of the testes and permanent sterility. It is 99 percent effective and very safe. The precise mechanism of action is unknown; the testicles atrophy over weeks to months following injection, resulting in a 70-90 percent reduction in testicular size in very young puppies and 50 percent in older dogs. Atrophy may not be symmetrical. Sterility is immediate in young puppies, but may take up to 60 days in postpubescent males. In most cases, Neutersol can be administered without sedation. An insulin syringe is used to administer a single injection into each testicle and animal discomfort is minimal. Neutersol does not abolish testosterone production. The obvious advantage is that it eliminates the need for anesthesia and surgery and saves substantial time. Suprelerin is a deslorelin implant that is approved for use in male and female dogs in Australia and New Zealand.

Compliance problems

Although virtually all animal shelters require sterilization of adopted pets, the compliance rate of owners, according to the American Humane Association, is about 60 percent despite implementation of spay/neuter contracts, coupons, other incentives and time-consuming follow-up. The American Veterinary Medical Association advises that all pets be neutered before adoption, including puppies and kittens as young as 8 weeks of age. The ideal age to spay/neuter dogs and cats is unknown. Currently, the most common age or the traditional age for recommending spaying/neutering is six months. This recommendation, however, is not based on research indicating that this is the ideal age to perform these procedures but was probably chosen because anesthetic and surgical techniques were less advanced at the time and surgical success was more likely in a larger patient. Based on previous peer-reviewed studies, we can now conclude that sterilizing young puppies and kittens is a medically sound practice, and is not associated with any serious medical or behavioral risks. In addition, early age spay/neuter offers many advantages including well-established, safe anesthetic and surgical techniques, shorter surgical and recovery times, and avoidance of the stresses and costs associated with spaying while in heat, pregnant or with pyometra. The procedure virtually eliminates the risk of mammary and testicular tumors.

Some veterinarians advocate a safe, humane and effective method of controlling existing populations of feral cats called "Trap, Neuter, Return" (TNR). Cats are trapped by caretakers, vaccinated, neutered and then returned to their "home" for release. The tip of the left ear is cropped to identify the cats as having been sterilized. This is the universal symbol for a sterilized free-roaming/feral cat.

Caretakers take responsibility for feeding and monitoring the health of the cats. TNR is not for colonies without caretakers. Studies have demonstrated that TNR is a successful method of controlling carefully monitored colonies by preventing growth due to reproduction.

When performed on a large scale, the success of such a program is felt at animal shelters where fewer cats are admitted for euthanasia. In addition, TNR has been shown to be more cost effective than trapping and euthanizing feral cats since most states require impoundment and holding prior to euthanasia and since private individuals frequently volunteer to trap cats for sterilization but not for euthanasia.

Relocation of feral cat colonies is almost always unsuccessful and is not advised since cats possess strong homing instincts and will try to return to their original home base.

TNR programs

It is important to recognize that a TNR program alone cannot solve the problem of free-roaming cats in the face of continuous emigration from the owned cat population. They do, however, hold great merit as a legitimate response to existing colonies of cats with caretakers and raise public awareness of the welfare issues facing cats in this country. TNR programs emphasize to communities that cats require and deserve responsible care, including sterilization, vaccination, identification, and regular feeding, watering and shelter. Clearly, the bulk of the effort in combating feline overpopulation and feral cats must focus on prevention.

Dr. Hoskins is owner of DocuTech Services. He is a diplomate of the American College of Veterinary Internal Medicine with specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200, or e-mail: jdhoskins@mindspring.com.