Feeding a dog a vegan diet is animal abuse
We may have tinkered with dogs and change their body and size frequently, but we have done nothing to change the internal anatomy and physiology of them. Dogs have the internal anatomy and physiology of a carnivore.
Dogs don't even produce the necessary enzymes in their saliva to start the break down process of carbohydrates and starches; amylase in saliva is something omnivorous and herbivorous animals possess in their mouth, but not carnivorous animals. This places a burden entirely on the pancreas, forcing it to produce large amounts of amylase to deal with the starch, cellulose, and carbohydrates in plant matter. The carnivores pancreas does not secrete cellulase to split the cellulose into glucose molecules, nor have become efficient at digesting and assimilating and utilizing plant material as a source of high quality protein.
As a result, most of the nutrients contained in plant matter - even pre-processed plant matter - are unavailable to dogs. This is why dog food manufacturers have to add such high amounts of synthetic vitamins and minerals (the fact that cooking destroys all the vitamins and minerals and thus creates the need for supplementation aside) to their dog foods. If a dog can only digest 40-60% of its grain-based food, then it will only be receiving 40-60% (ideally!) of the vitamins and minerals it needs. To compensate for this, the manufacturer must add a higher concentration of vitamins and minerals than the dog actually needs. The result of feeding dogs a highly processed, grain-based food is a suppressed immune system and the under-production of the enzymes necessary to thoroughly digest raw meaty bones.
Dogs have a relatively short foregut and a short, smooth, unsacculated colon. This means food passes through quickly. Vegetable and plant matter, however, needs time to sit and ferment. This equates to requiring longer, sacculated colons, larger and longer small intestines, and occasionally the presence of a caecum. Dogs have none of these, but have the shorter foregut and hindgut consistent with carnivorous animals. This explains why plant matter comes out the same way it came in; there was no time for it to be broken down and digested.
Those who insist dogs did not descend from wolves must disprove the litany of scientific evidence that concludes wolves are the ancestors of dogs. And, as I have already established, the wolf is a carnivore. Since a dog’s internal physiology does not differ from a wolf, dogs have the same physiological and nutritional needs as those carnivorous predators, which, remember, “need to ingest all the major parts of their herbivorous prey, except the plants in the digestive system.”