One of the best reasons to spay or neuter your pet is to avoid adding to the problem of pet overpopulation. Every day in the United States, thousands more puppies and kittens are born than are human babies. The result is that there are not enough homes for all these pets. The Humane Society of the United States (HSUS) estimates that between 6 and 8 million pets enter animal shelters each year. Of these pets, the HSUS believes that at least half — 3 to 4 million — are euthanized. Many of these animals are young and healthy.