To protect your dog's health and help control pet overpopulation, you should have your dog spayed or neutered by the time they reach 6 months old. The procedures have many additional health benefits as well.
For Female Dogs
Spaying prevents unwanted pregnancy, prevents cancer of the reproductive system, eliminates the potential for infections of the uterus later in life, and reduces the potential for breast cancer, especially if performed before the first heat cycle.
For Male Dogs
Neutering eliminates the potential for cancer of the testicles and reduces the risk of prostate cancer. The male is also no longer agitated by females and the strong hormonal drive to reproduce. He will tend to roam less, decreasing the potential to be hit by a car or otherwise injured, become lost or be involved in territorial fights.