Spayed

Neutering, from the Latin neuter ("of neither sex"), is the removal of an animal's reproductive organ, either all of it or a considerably large part. "Neutering" is often used incorrectly to refer only to male animals, but the term actually applies to both sexes. The male-specific term is castration, while spaying is usually reserved for female animals. Colloquially, both terms are often referred to as fixing. In male horses, castrating is referred to as gelding. Modern veterinary practice tends to use the term de-sexing.

Neutering is the most common method for the sterilization of animals. In the United States, most humane societies, animal shelters, and rescue groups urge pet owners to have their pets neutered to prevent the births of unwanted litters, which contribute to the overpopulation of unwanted animals in the rescue system. Many states require that all adopted cats, kittens, dogs, and puppies be sterilized before going to their new homes.

The practice has been advocated in radio and television commercials and on various shows, most notably the game show The Price is Right, whose host, Bob Barker, would end every episode with the catchphrase "Help control the pet population; have your pets spayed or neutered." After Barker's retirement, Drew Carey continued to sign off with his own message regarding spaying and neutering.

Besides being a birth control method, and being convenient to many owners, castrating/spaying has the following health benefits:

Various studies of the effects neutering has overall on male and female dog aggression have been unable to arrive at a consensus. A possible reason for this according to two studies is changes to other factors have more of an effect than neutering. One study reported results of aggression towards familiar and strange people and other dogs reduced between 10 and 60 percent of cases, while other studies reported increases in possessive aggression and aggression towards familiar and strange people, and more studies reported there was no significant difference in aggression risk between neutered and non-neutered males. For females with existing aggression, many studies reported increases in aggressive behavior and some found increased separation anxiety behavior. A report from the American Kennel Club Canine Health Foundation reported significantly more behavioral problems in castrated dogs. The most commonly observed behavioral problem in spayed females was fearful behavior and the most common problem in males was aggression. Early age gonadectomy is associated with an increased incidence of noise phobias and undesirable sexual behaviors.

...
Wikipedia