Pet Food Ingredients
Animal Protein
Dogs and cats are carnivores, and do best on a meat-based diet. The protein used in pet food comes from a variety of sources. When cattle, swine, chickens, lambs, or other animals are slaughtered, lean muscle tissue is trimmed away from the carcass for human consumption, along with the few organs that people like to eat, such as tongues and tripe.
However, about 50% of every food animal does not get used in human foods. Whatever remains of the carcass — heads, feet, bones, blood, intestines, lungs, spleens, livers, ligaments, fat trimmings, unborn babies, and other parts not generally consumed by humans — is used in pet food, animal feed, fertilizer, industrial lubricants, soap, rubber, and other products. These “other parts” are known as “by-products.” By-products are used in feed for poultry and livestock as well as in pet food.
The nutritional quality of by-products, meals, and digests can vary from batch to batch. James Morris and Quinton Rogers, of the University of California at Davis Veterinary School, assert that, “[pet food] ingredients are generally by-products of the meat, poultry and fishing industries, with the potential for a wide variation in nutrient composition. Claims of nutritional adequacy of pet foods based on the current Association of American Feed Control Officials (AAFCO) nutrient allowances (‘profiles’) do not give assurances of nutritional adequacy and will not until ingredients are analyzed and bioavailability values are incorporated.”3
Meat or poultry “by-products” are very common in wet pet foods. Remember that “meat” refers to only cows, swine, sheep, and goats. Since sheep and goats are rare compared to the 37 million cows and 100 million hogs slaughtered for food every year, nearly all meat by-products come from cattle and pigs.
The better brands of pet food, such as many “super-premium,” “natural,” and “organic” varieties, do not use by-products. On the label, you’ll see one or more named meats among the first few ingredients, such as “turkey” or “lamb.” These meats are still mainly leftover scraps; in the case of poultry, bones are allowed, so “chicken” consists mainly of backs and frames—the spine and ribs, minus their expensive breast meat. The small amount of meat left on the bones is the meat in the pet food. Even with this less-attractive source, pet food marketers are very tricky when talking about meat, so this is explained further in the section on “Marketing Magic” below.
Meat meals, poultry meals, by-product meals, and meat-and-bone meal are common ingredients in dry pet foods. The term “meal” means that these materials are not used fresh, but have been rendered. While there are chicken, turkey, and poultry by-product meals there is no equivalent term for mammal “meat by-product meal” — it is called “meat-and-bone-meal.” It may also be referred to by species, such as “beef-and-bone-meal” or “pork-and-bone-meal.”
What is rendering? As defined by Webster’s Dictionary, to render is “to process as for industrial use: to render livestock carcasses and to extract oil from fat, blubber, etc., by melting.” In other words, raw materials are dumped into large vat and boiled for several hours. Rendering separates fat, removes water, and kills bacteria, viruses, parasites, and other organisms. However, the high temperatures used (270°F/130°C) can alter or destroy natural enzymes and proteins found in the raw ingredients.
Because of persistent rumors that rendered by-products contain dead dogs and cats, the FDA conducted a study looking for pentobarbital, the most common euthanasia drug, in pet foods. They found it. Ingredients that were most commonly associated with the presence of pentobarbital were meat-and-bone-meal and animal fat. However, they also used very sensitive tests to look for canine and feline DNA, which were not found. Industry insiders admit that rendered pets and roadkill were used in pet food some years ago. Although there are still no laws or regulations against it, the practice is uncommon today, and pet food companies universally deny that their products contain any such materials. However, so-called “4D” animals (dead, dying, diseased, disabled) were only recently banned for human consumption and are still legitimate ingredients for pet food.
From here
http://www.api4animals.org/facts?p=359&more=1
do you mean your dog thinks that?