http://www.americanhumane.org/about-us/newsroom/fact-sheets/animal-shelter-euthanasia.html
However, American Humane is one of the founding members of the National Council on Pet Population Study and Policy. The mission of the National Council is to gather and analyze reliable data that further characterize the number, origin and disposition of pets (dogs and cats) in the United States; to promote responsible stewardship of these companion animals; and based on the data gathered, to recommend programs to reduce the number of surplus/unwanted pets in the United States.
Unfortunately, the most recent statistics published by the National Council are from 1997, and only 1,000 shelters replied to the survey at that time. Using the National Council's numbers from 1997 and estimating the number of operating shelters in the United States to be 3,500 (the exact number of animal shelters operating in the United States does not exist), these estimates were made:
* Of the 1,000 shelters that replied to the National Council's survey, 4.3 million animals were handled.
* In 1997, roughly 64 percent of the total number of animals that entered shelters were euthanized -- approximately 2.7 million animals in just these 1,000 shelters. These animals may have been euthanized due to overcrowding, but may also have been sick, aggressive, injured or suffering from something else.
* 56 percent of dogs and 71 percent of cats that enter animal shelters are euthanized. More cats are euthanized than dogs because they are more likely to enter a shelter without any owner identification.
* Only 15 percent of dogs and 2 percent of cats that enter animal shelters are reunited with their owners.
* 25 percent of dogs and 24 percent of cats that enter animal shelters are adopted.
It is estimated that approximately 3.7 million animals were euthanized in the nations shelters in 2008. This number represents a generally accepted statistic that is widely used by many animal welfare organizations, including the American Society for the Prevention of Cruelty to Animals (ASPCA).