Shelters

Every year, between 6 and 8 million dogs and cats enter US animal shelters. The Humane Society of the United States (HSUS) estimates that approximately 3 to 4 million dogs and cats are euthanized yearly in shelters across the United States. However, the percentage of dogs in US animal shelters that are eventually adopted and removed from the shelters by their new owners has increased since the mid 1990s from around 25% up to around 60-75% in the mid 2000s.

Info from: http://en.wikipedia.org/wiki/Dog