here is an interesting twist to it. this is taken from
http://www.petstyle.com/dog/health_w...section=health
While the physical structure of a dog's teeth, jaws, and intestinal system tell us they are natural carnivores, they also require some plant matter in their diet. Canine species in the wild ingest the stomach and intestines of their plant-eating prey. In doing so, they consume partly digested plant matter, which helps in digestion of the flesh and bone they feed upon.