Your dog must be in top physical condition. Toe nails must be short. A good quality food should be provided. The stresses placed on the dog mentally as well as physically may require a higher intake than normal. This doesn't mean over feed your dog.
Obesity is the worst enemy of the draft dog.
Never let your dogs get fat. All your training instincts must be in use while working with your dog. Be alert to his posture. When you have him in harness, and he is trying hard but unable to accomplish what you have asked him to do, STOP . You must solve the problem in such a way that he still has confidence in his own abilities.