Each year, millions of dogs and cats are killed in animal shelters. The cause of this problem is twofold: unaltered animals and puppy mills. Many believe that it is not necessary to spay or neuter dogs and cats. However, statistics show that one female cat can produce 370,092 cats in seven years, and one female dog can produce 67,000 dogs in six years. Spaying and neutering increases an animal’s life expectancy and reduces the number of animals put to death in shelters. The second cause of the problem are puppy mills—breeders who mass produce dogs in deplorable conditions and sell them to pet stores for resale. The female dogs are kept pregnant all year round and as a result are unhealthy. They are commonly inbred but are sold at premium purebred prices. CFA recommends adopting a pet from a shelter instead of buying one from a store and spaying or neutering that animal at the proper age.