Spaying and Neutering
If you are not going to show your dog, or if you are not an informed breeder, you should absolutely spay (remove the uterus and ovaries of a female) or neuter (remove the testicles of a male) your boxer. Indeed, there are far too many boxers in rescue to risk an accidental mating. If your boxer has an hereditary illness or tendency to an illness, spaying or neutering eliminates the likelihood of that illness being passed along. This includes the inherited heart disease, hip dysplasia, and possibly, early onset of thyroid disease.
Spaying and neutering are generally given as solutions to aggression and many other behavioral problems that they do not really address in all breeds. Regardless of whether you have your boxer pup spayed or neutered before sexual maturity, improper or insufficient training can still result in unacceptable behavior, including aggression. Don't use spaying or neutering as a substitute for training and behavioral management.
Spay/Neuter As Cancer Prevention
If you spay or neuter your boxer before sexual maturity, it is believed that you are reducing the risk of some kinds of cancers, particularly breast cancers in females. Studies also suggest that you are reducing the overall likelihood of cancer if you spay or neuter your boxer before sexual maturity. However, current research also suggests that if you spay or neuter your boxer before sexual maturity that they tend to grow taller, and may have some kind of joint problems later in life.
Probably the best time to spay a female if you do not wish to show her is before she has time to come into her first heat. Her breeder should be able to approximate the time when your bitch will come into heat. The best time to neuter a young male is probably after he is about 8 or 9 months old. He will have reached sexual maturity physically but not really had time to develop bad habits about it.
Later in life, intact females are more prone to developing condition. So again, you may want to spay your female boxer puppy before her first heat. Spaying a female while she is in her hormonal cycle is very hard on her, as the uterus and surrounding tissue is engorged with blood awaiting fertilization. Many reputable vets will not spay a bitch within sixty days of estrus in order to allow her glands and organs to go back to a normal size.
Spaying and neutering are surgical procedures that must be performed by a board-licensed veterinarian. These procedures are done under a general anesthetic. Spaying is easier on a younger female, but it is still a good idea for older females in order to prevent pyometra. Technically called an ovariohysterectomy, spaying is considered major surgery regardless of when it is done.
The neuter, which removes the testicles, especially if there is a retained testicle, such as in a monorchid or cryptorchid, is technically surgical castration.