What is the best age to have a female dog spayed?

In 1993, the American Veterinary Medical Association passed a resolution stating that it is best to spay when the dog is between eight and 16 weeks old. It is recommended to spay a dog before she has her first heat to reduce the risk of cancer significantly.

In years past, it was believed that allowing a dog to have a litter or a heat before spaying her was the most prudent thing to do. However, female dogs who have been allowed to mature sexually have an increased risk of developing mammary tumors. After two heats, the risk is as high as 26 percent. Removing the dog's gonads before she has a heat reduces her cancer risk to 0.5 percent.