The major counter argument to dogs being carnivores is that wolves happily eat the contents of their preys stomaches which are full of grasses and herbs. The fact is that the wolf eats the whole of the animal. The leaders of the pack get to choose the best parts to eat and the lower status wolves get the left overs. If a wolf eats the stomach contents it isn’t likely to be full of a succulent array of veggies.
If anything the contents are likely to be green, crushed and partly digested. They would also make up a relatively small part of the whole animal. You will also find an argument that wolves would typically only eat the whole stomach of smaller prey and would rather rip open large prey {stomachs|bellys) and eat the flesh wall of the stomach and the digestive juices, but not particularly the vegetable stuff.
You will also find that the nutrients available in common meats are highly sufficient in vitamins and minerals to sustain meat eaters - how else would meat eaters exist. Meat eaters do not require carbs in their diet as they process fat and protein from meat to regulate their blood sugar levels, and not taking sugars from veggies.
The Amylase enzyme is also said to be a corner stone of the carnivore argument. This chemical is used for breaking down some types of carbs and is present in the mouth and stomach of herbivore animals. In meat eaters it is typically present only in the stomach as it is not needed to pre digest vegetable parts in the mouth, as meat eaters don’t eat veggies. The chemical is not present in the domestic dogs mouth.
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