Everyday 10,000 humans are born in the U.S. and each day 70,000 puppies and kittens are also born. As long as these birth rates exist, there will never be enough homes for all the animals. As a result, millions of healthy, loving cats, dogs, kittens, and puppies face early deaths as a form of animal control. Others are left to fend for themselves against automobiles, the elements, other animals, and cruel humans. You can help just by spaying and neutering your pets, don't ever buy from a pet store, as almost every one of them uses some form of a puppy mill, and remind people to adopt from a shelter or a rescue. Thank you! (from here)
An intact dog can produce two litters a year of 6-10 puppies per litter, which means in six years, one female dog and her offspring could produce up to 67,000 dogs. An average of 40,000 cats/dogs are euthanized in Colorado each year (that's JUST Colorado!).