You also need to get extra protein into a subject for creatine to have any muscle building effect, or so I've always been led to believe. If you were to use any supplements in that way, you'd have to put a lot of work into the dog, far more than you'd normally need to get the desired results. It wouldn't be a matter of simply giving the dog the stuff and just carrying on as per usual. You'd have to vastly increase the amount of exercise and the amount of food...
I can't see the point personally. Dogs have been doing the job fine without it, and IMO the only people who'd consider using i