Sadly, nearly 8 million of those animals are euthanized because there are not enough homes for them all. Millions more never make it to a shelter. Spayed or neutered dogs and cats live longer, healthier lives. It greatly reduces cancer and other hormone-related medical disorders in dogs and cats Neutered animals are less likely to roam, bite or fight. Animals have no psychological need to reproduce.
Neutered cats are less likely to spray and mark territory.
Spaying a female dog or cat eliminates its heat cycle. Females in heat often cry non-stop, are nervous and attract unwanted male animals. Irresponsible breeding breeds more cases of dog attacks.