Altering Your Dog
Behavior: Contrary to popular belief, spaying and neutering has not been proven to alter your dog's behavior, so it will NOT provide a replacement to proper exercise and discipline of your dog! That said, neutering will curb fighting and roaming brought on by sexual frustration in males, and spaying will prevent unpleasant heat cycles and the odd behavior and mess that comes with heat cycles in females. Sterilization procedures will, in general, cause a reduction in a dog's activity level, which means a more manageable dog for the average pet owner.
Health: Spaying a female dog will eliminate the risk of pyometra, a serious and sometimes even fatal disease necessitating expensive emergency surgery. It will also greatly reduce the risk of mammary cancer in females. Neutering will eliminate the risk of testicular cancer in males.
Health: Altering is associated with a slightly increased risk of obesity and obesity associated diseases; keep your dog active and watch their diet to prevent obesity and you'll enjoy a much happier, healthier pet. Remember that neutered male dogs are not necessarily immune to certain male disorders like prostate cancer and other cancers; make sure to have your male dog regularly examined by a veterinarian, especially as they reach middle to old age.
When to Alter?
Shelter Animals: All shelter animals leave the shelter spayed or neutered. This has been proven to be the only way to reliably keep adopted animals from contributing to pet overpopulation.
Male Dogs: Male dogs should be neutered before puberty at approximately six months of age. They can be safely neutered provided they are at least two pounds and over eight weeks old.
Female Dogs: Female dogs should preferably be spayed after three months and before six months of age, especially if they are going to be a large breed dog. Spaying a large breed dog before three months of age may contribute to a slightly increased risk of urinary incontinence.
The Bottom Line
Unless you own a healthy pedigreed dog AND actively compete with your dog in conformation or performance AND your dog has proven that they are an excellent example of their breed in those areas, you should NOT breed your dog! There is absolutely NO VIABLE health or behavior reason to allow your female dog to have "just one litter" before spaying her or to allow your male dog to keep his testicles because you as the owner are insecure about male body parts (if it's really a problem, there are, in fact, prosthetic testicles that can be inserted at the time of neutering)! These arguments arose from people placing human emotions on their pets -I promise you, your dog will NOT miss their reproductive organs at all!
A harsh judgment? Well, if you think so, I invite you to visit your local humane society on euthanasia day (Tuesdays and Thursdays where I'm from) and feast your eyes on the bodies of dogs that had to be destroyed because there were no homes to be found for them. Don't be surprised if there are (pardon me) piles of them, particularly pitbulls and powerful breeds.
Still can't resist the thought of letting your dog produce a litter of puppies? Go back to that humane society and get your puppy fix by playing with the little ones in the shelter, or better yet, foster a litter of puppies until they reach adoption age; don't let your dog produce more puppies and jeopardize other dogs' chances of finding a forever home.