My vet was active in a research intended to see the effects of spaying and neutering at different ages. They found that altering before the dog's growth plates closed gave the dog a higher chance of bone cancer as opposed to the lower chance of the other cancers it could get from allowing it to mature sexually. Cancer is becoming a common thing in Belgians, and I have yet to see a case of any testicular/mammary cancer in a Belgians, but plenty of bone cancer. Therefore, I choose to wait until the dog is done growing -- no matter the breed, for me.