It is not happenstance that four of the top five major pet food companies in the United States are subsidiaries of major multinational food production companies: Colgate Palmolive (which produces Hills Science Diet), Heinz, Nestle, and Mars (see The Corporate Connection). From a business standpoint, multi-national food companies owning pet food manufacturers is an ideal relationship. The multinationals have captive market in which to dump their waste products, and the pet food manufacturers have a direct source of bulk materials. Both make a profit from selling scraps that originate from places far worse than the dinner table. In his 1986 book Pet Allergies, veterinarian Al Plechner sums up what goes into companion animals' food: Condemned parts and animals rejected for human consumption are routinely rerouted for commercial pet foods. A similar fate applies to so-called 4-D animals. These are food animals picked up dead, or that are dying, diseased, or disabled, and do not meet human-food qualifications. They are processed straightaway for companion animal consumption. Little goes to waste. Says Plechner, food processing refuse of all sorts winds up in your animals' dinner bowls. Moldy grains. Rancid foods. Meat meal. The latter is ground-up slaughterhouse discards often containing disease-ridden tissue and high levels of hormones and pesticides, the very things that may have contributed to the death of the steer or hog. A decade later, his words still apply. When cattle, swine, chickens, lambs, or other animals meet their ends at a slaughterhouse, the choice cuts -- lean muscle tissue and organs prized by humans -- are trimmed away from the carcass for human consumption. Whatever remains of the carcass (bones, blood, pus, intestines, ligaments, subcutaneous fat, hooves, horns, beaks, and any other parts not normally consumed by humans) is, according to the pet food industry, perfectly fit as a protein source for cat and dog food.

The Pet Food Institute, the trade association of pet food manufacturers, acknowledges in its 1994 Fact Sheet the importance of using byproducts in pet foods as additional income for processors and farmers. The purchase and use of these ingredients by the pet food industry not only provides nutritional foods for pets at reasonable costs, but provides an important source of income to American farmers and processors of meat, poultry, and seafood products for human consumption. Many of these remnants are indigestible and provide a questionable source of nutrition. The amount of nutrition provided by meat byproducts, meals, and digests varies from vat to vat of this animal protein soup. A vat filled with chicken feet, beaks, and viscera is going to make available a lower amount of protein than a vat of breast meat. James Morris and Quinton Rogers, professors with Department of Molecular Biosciences at the University of California at Davis Veterinary School of Medicine, assert that there is virtually no information on the bioavailability of nutrients for companion animals in many of the common dietary ingredients used in pet foods. These ingredients are generally byproducts of the meat, poultry and fishing industries, with the potential for wide variation in nutrient composition. Claims of nutritional adequacy of pet foods based on the current AAFCO nutrient allowances (profiles) do not give assurances of nutritional adequacy and will not until ingredients are analyzed and bioavailability values are incorporated. Meat byproducts, the catch-all term of the pet food industry, is a misnomer because these byproducts contain little if any meat. Byproducts contain little if any meat. Byproduct are animal parts leftover after the meat has been stripped from the bone. Chicken byproducts include heads, feet, entrails, lungs, spleens, kidneys, brains, livers, stomachs, noses, blood, and intestines free of their contents. What the pet food manufactures fail to mention is that most byproducts, digests, and meals are also filled with other substances, such as cancerous tissue cut from the carcass, plastic foam packaging containing spoiled meat from supermarkets, ear tags, spoiled slaughterhouse meat, road kill, and pieces of downer animals.