A Dog Needs Protein

On the back of your dog food package, it should tell you how much protein is in the food. If the first five ingredients listed are grains this means the  protein in the dog food is mostly from plants.
Dogs need animal protein.  When a dog doesn't get the right amount of animal protein in his diet, many problems can occur.
Some symptoms from lack of animal protein are: skin or ear infections, cancer, lack of pigementation,weakened immune system, vomiting, diaherrea, poor appetite, agression, timidity, tail chasing, and they may have a hard time healing their wounds.
Source:
The Complete Idiot's Guide to a Well -Trained Dog by Jack and wendy Volhard.
I also learned some of this information from a vet who came to my 4-H Dog Club meeting and talked about dog nutrition.