For your dog to be in good physical shape, and at the end of a day content be sure he gets enough exercise for the type of dog he is. If unsure and owning a pure bred dog, check information on your breed to find out what is good for the dog, and why. If you have a mutt, or a mixed breed, simply know that to be healthy and happy, all living things need to move. It almost makes one weep for many dogs, who only get a walk around the block on a leash a few times a day.
