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.
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
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.