Pet food is a specialty food for domesticated animals that is formulated according to their nutritional needs. Pet food generally consists of meat, meat byproducts, cereals, grain, vitamins, and minerals. In the U.S. about 300 manufacturers produce more than 7 million tons of pet food each year, one of the largest categories of any packaged food. Pet owners can choose from more than 3,000 different pet food products, including the dry, canned, and semi-moist types, as well as snacks such as biscuits, kibbles, and treats. In the 1990s, this $8-billion industry feeds America's 52 million dogs and 63 million cats.
Commercially produced pet food has its origins in a dry, biscuit-style dog food developed in England in 1860. Shortly afterwards, manufacturers produced more sophisticated formulas, which included nutrients considered essential for dogs at the time. At the beginning of the 20th century, pre-packaged pet foods were also available in the U.S. Initially they consisted primarily of dry cereals, but after World War I, dog food made of canned horse meat was available. The 1930s ushered in canned cat food and a dry, meatmeal type of dog food. Some innovations by the 1960s were dry cat food, dry expandedtype dog food, and semi-moist pet food.
Beginning in the 1980s, trends in the pet food market included greater demand for dry foods and less for canned foods. Research suggested that a soft diet of canned dog food led to gum disease more quickly than did dry food. In general, the growing health-consciousness of the public led to an increased interest in more nutritious and scientific formulas for pet foods, such as life-cycle products for younger and aging pets, and therapeutic foods for special health conditions of the pet, such as weight loss and urinary problems. Pet food producers were also more inclined to use less fatty tissue and tallow and more protein-rich tissue. Finally, the pet snack category grew in popularity with products like jerky snacks, sausage-shaped pieces, biscuits, and biscuit pieces called kibbles.
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.
Except for the ingredients, the general manufacturing process for pet food is similar to that for processed food. The flesh products used in pet foods must first be rendered, or processed, to separate the water, fat, and protein components, including soft offals (viscera) and hard offals (e.g. bones and hoofs). Generally, meat is rendered by out-side companies and shipped to pet food manufacturers. The meat products intended for canned food must be delivered fresh and used within three days. Frozen meat products may be used for dry foods.
The manufacturing process entails grinding and cooking the flesh and flesh byproducts. Next, the meat is mixed with the other ingredients, and if the recipe requires, the mixture is shaped into the appropriate forms. The finished product is filled into containers and shipped to distributors.
Innovations in pet food processing and packaging have led to better quality products with longer shelf life. Canned dog foods that are vacuum packed have a shelf life of three to five years and are very stable with little or no loss in nutritional value. Dry dog food, on the other hand, has a shelf life of only 10 to 12 months and requires the addition of preservatives, though some manufacturers are using natural preservatives such as vitamins E and C.
Rendering the meat
- 1 Generally, rendering is performed by meat processors. Rendering entails rupturing fat cells, either by heat or enzymatic- and solvent-extraction, and then drying the residue.
Grinding and pre-cooking the meat
- 2 The meat products are coarsely ground to the desired texture.
- 3 To facilitate further processing, the ground meat is cooked in a continuous cooker with live steam at the appropriate temperature.
- 4 The flesh products are reground after initial cooking to produce a more uniform consistency. For semi-moist or chunky foods, the batches are deliberately cooked unevenly to create the desired chunky texture.
Blending and shaping
- 5 The meat mixture is blended with other ingredients such as cereal grains, vitamins, and minerals.
- 6 Dry and semi-moist foods are usually heated so the mixture will partially dextrinize, or thicken, the starch. To achieve the marbled-look of real meat, the meat mixture may be cooked unevenly and half of the batch colored red and the other white. Semimoist foods must be stabilized to retain the proper amount of moisture in the dry and semi-moist parts of the food.
- 7 Dry and semi-moist foods may be extruded under high pressure through a device with orificed plates to obtain the shape and size of the specific product, for instance, the form of biscuits, kibbles, meat-balls, patties, pellets, or slices. An alternative to extrusion is to gelatinize and expand the mixture. For marbled meat, the mixture of red and white meat is extruded together and broken into chunks.
Packaging and labeling
- 8 Measured amounts of the product are packaged into appropriate containers. Dry foods are poured into pre-printed containers. Moist canned foods are vacuum sealed to reduce the oxygen content and prevent spoilage of fats in the food.
- 9 Cans of pet food are sterilized by passing them through a retort, or heating chamber. The retort may be either a batch or continuous hydrostatic type. The cans are heated to about 250°F (121°C) for 80 minutes, though the cooking temperatures and times depend on the contents, steam pressure, and can size.
- 10 The cans are quickly cooled to about 100°FO (38°C). Next, the cans are dried and labeled.
- 11 The containers are packaged into corrugated cardboard boxes or shrink-wrapped with plastic in corrugated cardboard trays. The pet food is ready fot shipping to distributors.
Pet food manufacturers must conform to the rules and regulations set by several agencies at the federal and state levels, including the Food and Drug Administration (FDA), Federal Trade Commission (FTC), and U.S. Department of Agriculture (USDA). The USDA controls meat quality and determines which animals can be used in pet foods. The FDA regulates ingredients by setting maximum and minimum limits on certain nutrients and by banning the use of medications or antibiotics in foods, since pet food is sometimes accidentally eaten by children. The job of the Association of American Feed Control Officials (AAFCO), a non-governmental advisory group with representatives in each state, is to register the 3,000 brands and sizes of pet food.
The "guaranteed analysis" statement found on pet food labels was created nearly a century ago when some manufacturers used undesirable ingredients like sand or lime-stone to add weight to their pet food. The guaranteed analysis ensures minimum percentages of crude protein and crude fat and maximum percentages of crude fiber and moisture. The term "crude" refers to a method of testing the elements. Other guarantees may include minimum amounts of calcium, phosphorus, sodium, and linoleic acid in dog food, and ash, taurine, and magnesium in cat food. The maximum allowable moisture for canned food is 78%, while dry foods may contain as much as 12% moisture.
Proper labeling of pet foods is required to provide accurate information to the purchaser. Guidelines are set by the FDA's Center for Veterinary Medicine and the AAFCO. Six basic elements should be on the label: the product name, net weight, name and address of the manufacturer or distributor, guaranteed analysis, ingredient list, and nutritional information. The product name should accurately describe the contents and adhere to the "percentage" rules. The "95%" rule requires that if the product name suggests that meat, poultry, or fish is the primary ingredient, as in "Barbara's Beef Dog Food," it must contain 95% or more of that ingredient, excluding water used in processing. If two meat ingredients are listed as the primary ingredients, the two together must equal 95%.
The "25%" rule, or "dinner" rule, applies to items such as "chicken dinner," "meat entree," and terms like platter, formula, nuggets, and so on. It requires that the food listed must make up between 25 and 95% of all ingredients by weight. If more than two ingredients are in the name, each must be at least three percent in weight and the primary ingredient must be listed first, as all the ingredients on the label must be listed in predominance by weight.
A third rule is the "three percent" rule, or the "with" rule, which applies to minor ingredients listed on the label. For example, "Charlie's Chicken Cat Food with Cheese" should contain at least three percent cheese. Finally, the "flavor rule" requires that if a flavor ingredient, such as meat meal, is included in the name it must be detectable. To prevent misleading customers, the word "flavor" must be in the same size and style as the corresponding ingredient. Any pictures on the label must not be misleading either.
All the ingredients should correspond to the specific names listed in the Official Publication of the AAFCO. Any preservatives, stabilizers, colors, and flavorings must conform to the GRAS rule, "Generally Recognized as Safe." The term "natural" should not be applied to products containing artificial flavors, colors, or preservatives.
Calories per serving and per container should be listed in much the same manner as foods for human consumption, in kilocalories per kilogram. Package codes must be printed on all containers.
Other associations also monitor pet foods and evaluate their effects on pets, such as the American Animal Hospital Association (AAHA), the American Veterinary Medical Association (AVMA), and the Pet Food Institute (PFI).
Where To Learn More
Ockerman, H.W. and C.L. Hansen. Animal By-Product Processing. VCH Publishers, 1988.
Corbin, James. "Promote Product Acceptance with a Lesson on Pet Food Labels." Pet Product News, July 1993, p. 40.
Ducommun, Debbie. "The Dog Food Debate." Pet Product News, May 1994, p. 45.
Dzanis, David A. "Understanding Pet Food Labels." FDA Consumer, October 1994, p. 10.
Eckhouse, John. "How Dogs and Cats Get Recycled into Pet Food," Part One. The San Francisco Chronicle, February 19, 1990, p. Cl.
—. "Pet Food Is Big Business," Part Two. The San Francisco Chronicle, February 20, 1990, p. B1.
McDermott, Michael J. "Pedigreed Pet Foods." Food & Beverage Marketing, May 1991, p. 20.
Presley Noble, Barbara. "All about Dog and Cat Food: Will the American Pet Go for Haute Cuisine?" The New York Times, December 16, 1990, p. 5.
"Pet Food Institute Fact Sheet, 1994." Pet Food Institute, 1200 19th St., NW, Ste 300, Washington, DC 20036. (202) 857-1120.