The primary ingredients in pet food are byproducts of meat, poultry, and seafood, feed grains, and soybean meal. Among the animals used in rendering are livestock, horses, and house pets which have been put to sleep. The National Animal Control Association estimated that each year about 5 million pets were shipped to rendering plants and recycled into pet food during the 1990s. They are generally listed as meat or bone meal in the ingredient lists.
The animal parts used for pet food may include damaged carcass parts, bones, and cheek meat, and organs such as intestines, kidneys, liver, lungs, udders, spleen, and stomach tissue. Cereal grains, such as soybean meal, corn meal, cracked wheat, and barley, are often used to improve the consistency of the product as well as to reduce the cost of raw materials. Liquid ingredients may include water, meat broth, or blood.Salt, preservatives, stabilizers, and gelling agents are often necessary. Gelling agents allow greater homogeneity during processing and also control the moisture. They include bean and guar gums, cellulose, carrageenan, and other starches and thickeners. Palatability can be enhanced with yeast, protein, fat, fish solubles, sweeteners, or concentrated flavors called “digests.” Generally, artificial flavors are not used, though smoke or bacon flavors may be added to some treats. Most manufacturers supplement pet foods with vitamins and minerals, since some may be lost during processing.
Ingredients vary somewhat depending on the type of pet food. The basic difference between canned and dry pet foods is the amount of moisture. Canned food contains between 70 and 80% moisture, since these are generally made from fresh meat products, while dry pet food contains no more than 10%. Additional ingredients used for dry foods include corn gluten feed, meat and bone meal, animal fats, and oils. For a meat-like texture, dry foods require more amylaceous, or starch ingredients; proteinaceous adhesives, such as collagen, albumens, and casein; and plasticizing agents. Semi-moist pet foods usually require binders, which come from a variety of sources, such as gels, cereal flours, sulfur-containing amino acids, lower aLkyl mercaptans, lower alkyl sulfides and disulfides, salts, and thiamin. Semimoist products may also incorporate soybean flakes, bran flakes, soluble carbohydrates, emulsifiers, stabilizers, and dried skim milk and dried whey.
Antioxidants are often used to retard oxidation and rancidity of fats. These include butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), and tocopherol. To prevent mold and bacterial growth, producers use either sucrose, propylene glycol, sorbic acid, or potassium and calcium sorbates.