Taken from:
http://www.i-love-cats.com/Health/spay.htm
What is Spaying?
A spay (ovariohysterectomy) is the surgical removal of the uterus and ovaries from the abdomen of an animal.
What is the purpose of spaying?
The spay is the only foolproof method of birth control for female cats, and it is a permanent method.
Will spaying eliminate heat cycles?
Spayed animal no longer goes through heat cycles. Female cats normally come into heat several times a year. Spaying ends several problems associated with the heat cycle, including spraying urine and the necessity of confining females to prevent the approaches of persistent males. Spaying also prevents such irritations as a howling cat in heat.
Are there other good reasons for spaying?
The risk of mammary cancer is reduced if a cat is spayed before its first heat. Also spayed pets cannot develop pyometra, a serious uterine infection. Finally, difficult pregnancy and delivery in older cats or ill cats is prevented.
Do cats gain weight after spaying?
Your cat will not gain weight, if you provide a balanced diet and encourage regular exercise.
Should cats have at least one litter before being spayed?
No. Your cat does not need to have a litter of kittens to mature.
What is Neutering?
Neutering (castration) is the surgical removal of the testicles from the scrotum of an animal.
What is the purpose of neutering?
Neutering is the primary method of sterilizing male cats.
What are other benefits of neutering?
Neutering an immature cat usually prevents development of mating behavior and the obnoxious habit of spraying urine to mark territory around the house and yard.
An unneutered cat cannot control its mating instincts. Given freedom to wander, such an animal may become hurt or lost, and is almost certain to be responsible for unwanted litters. Humane societies cannot place all unwanted animals; millions must be put to sleep. Countless others are abandoned.
See your veterinarian!
Discuss your questions about breeding and birth control with your veterinarian.