The studies also found that the majority of pet owners who surrender their animals to shelters are under 30 years of age and that more dogs are taken to shelters than cats and all other animals combined.

"Euthanasia of domestic pets in the United States is an epidemic," Salman said. "These studies give us the first glimpse of why so many pets are entering shelters and what happens once they are surrendered by their owners."

About 1,000 shelters in the United States responding as part of Shelter Statistics Survey accepted an estimated 4 million pets each year in 1994, 1995 and 1996. Of those sent to the reporting shelters that participated in the study, about 64 percent--or 8.2 million pets--were euthanized.

The survey also revealed that, on average, 42.5 percent of pets that entered animal shelters were submitted by animal control authorities and nearly 30 percent were surrendered by their owners. The remainder were relinquished by other sources. Twenty-four percent, or 3 million, of the animals taken to shelters over the three-year period were adopted by new families. Only 10 percent, or 1.2 million, were reclaimed by their owners.

The studies mark the first, large-scale national effort to quantify pet overpopulation in the United States and identify reasons why pet owners relinquish their animals. With this information, the National Council on Pet Population Study and Policy hopes to develop strategies to curb the epidemic of pets entering animal shelters.

Of the 70 reasons pet owners could cite for relinquishing their pets, 15 percent said their animals were ill or old and needed to be Euthanized; 7 percent said they were moving; 5 percent felt they had too many animals; 4 percent said owning a pet cost too much; and 3.5 percent said the animals had soiled the house.

In addition, the majority of respondents--62 percent--were under 30 Years of age and 52 percent had at least finished high school.

"Some of the reasons pet owners cited for giving up their pets to shelters may be resolved through educational or other types of programs," Salman said. "Most of the problems are really not with the animals, but rather with pet owners who may not be knowledgeable enough about or prepared for the realities of owning a pet."

The council is composed of 11 non-profit and scientific organizations. Members include the American Animal Hospital Association, American Humane Association, American Kennel Club, American Society for Prevention of Cruelty to Animals, American Veterinary Medical Association, Association of Teachers for Veterinary Public Health and Preventative Medicine, Cat Fanciers Association, The Humane Society of The United States, Massachusetts Society for the Prevention of Cruelty to Animals, the National Animal Control Association and the Society of Animal Welfare Administrators.

Colorado State University's Epidemiology and Animal Disease Surveillance Systems is the scientific co-ordinator for the council. The center is based in the department of environmental health in the College of Veterinary Medicine and Biomedical Sciences.