Almost all rendered meats have synthetic preservatives added as stabilizer, but manufacturers aren't required to list preservatives they themselves haven't added. Premixed vitamin additives can also contain preservatives. In the 1003 Journal of the American Veterinary Medical Association, veterinarian Philip Roudebush reported finding low concentrations of synthetic antioxidant preservatives in all analyzed samples of products labeled as chemical free or all-natural. Other types of additives depend on whether the pet food is semi-moist, dry or canned. Propylene glycol was frequently used in cat food until it was pulled in 1992 for causing a variety of health problems.
Processing greatly alters the nutritional value of the food ingredients.
Heating, freezing, dehydrating, canning, extruding, pelleting, baking and so forth, are so commonplace that they are simply thought of as synonymous with food itself. Because the ingredients that pet food companies use are not wholesome, and harsh manufacturing practices destroy what little nutritional value the food may have had in the first place, the final product must be fortified with vitamins and minerals. Yet in 1994, feed tests conducted by the New York State Agriculture Department showed 7 percent of all pet foods analyzed failed chemical analyses for guaranteed nutrients. Other states report similar findings, with failure of analyzed feed ranging from to 12 percent. Although manufacturers clam that millions of companion animals can thrive on a diet consisting of nothing by commercial pet food, research and an increasing number of veterinarians implicate processed pet food as a source of disease or as an exacerbating agent for a number of degenerative diseases.