Spent brewery waste, grain byproducts, feathers, fur, and hooves -- all approved for dog food. Old boots pass the pet-food tests as suitable ingredients as well, though they are completely indigestible. In other words, the pet-food industry interprets dogs' dietary needs as anything people want to throw into a kibble extruder or seal in a can.
Let's get evolutionary facts straight. Dogs are wolves. Domestic cats are closely related to wild, desert cats. Teeth of dogs and cats are those of carnivores, who tear meat off carcasses and chew up tough muscles of animal prey. Sharp, pointed carnivore teeth are not like herbivore teeth, which are broad and flat to grind grains and vegetable foods. Carnivore teeth evolved for a diet of animal flesh. Herbivore teeth evolved for food from grazing.
Cat and dogs have carnivore digestive systems. Carnivore guts are highly acidic and short. Meats and bones are digested and waste is eliminated quickly. Herbivores have long, complex digestive tracts to process vegetable matter over many hours through multiple organs. Carnivores do not process grains and vegetable matter properly, because that's not an appropriate diet for their teeth or digestive tracts.
The pet-food industry and veterinarians, who deny evolutionary facts, want pet owners to believe that dogs and cats can thrive on a largely herbivore diet of grains and other starches. Why? Because starches are cheap byproducts from human food processing by the same companies that make pet foods. Pet food is an enormously profitable byproduct for global food companies (Mars, Nestle, and P & G make a lot more than candies, cereals, and boxed meals).
We know that processed foods are poor substitutes for fresh foods in human diets. Just imagine what the waste products from human food processing do to the health of carnivorous pets.
The pet-food industry promotes AAFCO trials as the gold standard for pet food quality, when in fact AAFCO trials test the lower limits of how little animal protein and fat will keep dogs and cats alive for 6 months. Used as a recipe for pet food, AAFCO trials are, instead, a prescription for lingering death.
As long as the pet food industry can deny that cats and dogs are carnivores, they will continue to profit from foods that sicken and eventually kill pets. Veterinarians, who largely support their benefactors -- the pet food companies -- will continue to profit from the illnesses the starchy, commercial pet foods cause. It is an unholy alliance.