I'm not feeding puppy food. Adult all stages. When I had GSD's on puppy food, they would get painful joints around 4-6 months, sometimes longer. It's called something but I can't think of it right now. They get over it but they will limp around for a while. So exercise should be kept an a minimum til it passes. Something about bones growing at a faster rate or something like that. It's been a long time since I've had pups til now. Anyway, the breeder I got my pup from said she NEVER feeds puppy kibble, it's too rich, too high in calories for GSD's.
And now I wonder if the sore joints were the cause of puppy food??? Growing faster than they needed. IDK.... but something to think about.