An unaltered female cat may go through several heat cycles each year. Intact female dogs usually go into heat two times each year. A cat becomes fertile well before she reaches one year old, which means she could produce dozens of litters of kittens during her lifetime. Cats in heat have loud vocalizations and can act aggressively to try to gain the attention of male cats.
Spaying a dog reduces her desire to roam free. If an unneutered neighbor male dog gets near a spayed female dog, he won’t attempt to mate with her. In addition to preventing litters of puppies and kittens that may not find a home, spaying a cat or dog decreases her risk of developing uterine, ovarian, and mammary gland cancer. The risk decreases the most for dogs and cats who have had surgery before they would have gone into heat for the first time.