From ANIMAL PEOPLE, July/August 2006:
The U.S. regions where the first low-cost and free dog and
cat sterilization programs started, between 30 and 50 years ago,
still are making the fastest progress in reducing the numbers of dogs
and cats killed in animal shelters.
The 13th annual ANIMAL PEOPLE projection of the U.S. shelter
killing toll shows that the rate of killing per thousand humans
appears to have fallen back to the low of 14.8 that was achieved in
2000-2001, after a steep rise in 2001-2002. Because the U.S. human
population and the numbers of dogs and cats kept by humans have all
increased, the current annual toll of about 4.38 million dogs and
cats killed in shelters is still about 180,000 higher than the toll
of five years ago.