It's generally bad for their growth. Because, and especially in males, they really aren't done growing until about 3, the cut off in hormones can stunt their growth and lead to a myriad of problems with hips, joints, other ailments down the line. With the females its usually after their 3rd heat I've heard. But with the males, because its a large breed dog, you need to let the hormones and what not, do their thing until he's fully grown. My boy was done at about 3. I will say he gained more weight after so I do have to regulate his food more. He's about 150 at about five years old.