Should I avoid animal by-products in my pet's food?

Animal by-products are often the parts of the animal that Americans don't like to eat—organ meats, blood and bone from mammals—and can also include necks, feet and underdeveloped eggs from poultry. (Horns, hair, teeth, hooves, intestinal contents and feathers are prohibited.) By-products can add flavor and nutrients to pet food. In fact, these ingredients often have higher levels of iron, copper, calcium, vitamin A, B12 and many other essential nutrients than muscle meat.