While a vasectomy renders a male cat sterile, it does not affect testosterone levels as long as the spermatic artery is kept intact. A vasectomized cat, in other words, can mate, but cannot father kittens. This procedure is rarely used for domestic male cats, because a vasectomized male cat will still be territorial, still fight, still wander, and still spray urine that has a very strong odor. Vasectomy is still a valid alternative for population control in feral cat colonies, however. The best time to alter your pet is before the animal reaches puberty.
Many experts feel that six months of age is an ideal time to spay or neuter.
However, there have been numerous studies done that show that healthy kittens spayed or neutered as young as six weeks of age do quite well. The recovery of such young kittens is very quick, and to date, no negative significant concerns have been found. Spaying and neutering kittens and puppies that are healthy at a very young age is becoming a growing trend that has been endorsed by major humane organizations including the Humane Society of the United States, the American Veterinary Medical Association, the American Humane Association, and the Cat Fanciers' Association. Some people still feel that a kitten should be larger and stronger before undergoing the general anesthesia required to perform the surgery, and to allow more time for the urinary tract system to develop. Consult with your veterinarian and other veterinary health professionals that you trust to help you determine the right age for your kitten or cat.