(For the most current description of the pet food manufacturing process visit: www.petfoodinstitute.org )
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
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
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).
How Pet Food Is Made
By Pet Food Institute – Washington, DC
Many of the same processes used to make food people eat are also used to make pet food: baking for treats; canning; extrusion for dry kibble, which is also used to make many breakfast cereals; sous-vide, which is a gentle cooking similar to what is used for some pates; and other techniques.
Dry kibble provides the largest portion of calories for America's pets. Kibble accounts for more than 60% of all cat food and dog food sales in the United States. Dry products are available in packages ranging from boxes of just over a pound to large bags weighing 40-50 pounds.
Dry products are made through one of several different processes:
- Extrusion/Expansion (similar to process used to make certain breakfast cereals)
Wet Pet Food
The most familiar form of wet pet food is sold in a can. Innovation in manufacturing processes can led to the development of new wet products sold in trays and pouches, similar to certain products people eat.
How Dry Pet Food Is Made
While there are numerous ways to making dry pet food, the most commonly used process is extrusion. This process was adapted for making pet food in the 1950s based upon technology used to make puffed breakfast cereals. The diagram on Making Pet Food by Extrusion illustrates the process:
- Ingredients are brought together in a mixer. Dry ingredients may be ground prior to introduction to wet ingredients. Once mixed together, they form a moist dough.
- The dough is heated in the preconditioner prior to introduction to the extruder.
- The extruder, essentially a giant meat grinder, is where the primary cooking phase for dry extruded pet food products occurs. The dough is cooked under intense heat and pressure as it moves toward the open end of the extruder. At the end of the extruder, hot dough passes through a shaping die and knife (similar to the action of a meat grinder) where the small pieces expand rapidly into kibble once they are under standard air pressure.
- Kibble is dried in an oven until its moisture content is low enough to make it shelf stable like a cookie or cracker. The drying oven is followed by a cooling phase.
- After cooling, kibble may pass through a machine that sprays on a coating, which is generally a flavor enhancer.
- Packaging (bags, boxes, pouches, etc.) is filled during the last step to precise amounts to meet the weight advertised on the label. The final result is finished pet foods or treats.
How Wet Pet Food Is Made
Pet food companies are required to follow the same federal regulations for making wet pet food products (such as products in cans, pouches and trays) that human food companies must follow for low acid foods (21 CFR Part 113). The diagram Making Wet Pet Food illustrates the process by which products sold in cans, pouches, trays and similar containers are made:
- Ingredients are incorporated in a mixer.
- Clean empty containers (cans, pouches, trays, etc.) are filled to precise amounts to meet the weight advertised on the label.
- Lids are applied, if used, and containers are sealed.
- Sealed containers are cooked at a specified temperature, for a desired time, to destroy all living organisms that may be present (bacteria, viruses, mold) that could otherwise grow in the sealed container and cause illness in people or pets.
- Once cooled, labels are applied to containers, resulting in finished wet products.
Regulation of Pet Food
Pet food products are among the most highly regulated products in grocery stores. Federal and state laws and regulations apply to various aspects of pet food including ingredients, manufacturing processes and labeling. Virtually all state pet food laws and regulations are based upon the work of the Association of American Feed Control Officials. AAFCO is an organization of state officials who regulate animal feed, which includes pet food. Members of AAFCO come together to develop standard ingredient definitions; nutritional requirements; labeling and other guidelines; and model laws and regulations for the animal feed/pet food sector. AAFCO's work helps promote uniform laws and regulations for pet food from state to state, which effectively ensures consumer protections nationwide and promotes interstate commerce.
At the federal level, pet food is regulated by the U.S. Food and Drug Administration, U.S. Department of Agriculture and Federal Trade Commission. Both the FDA and FTC have authority over labeling and advertising claims. In addition to the states, FDA regulates pet food ingredients and finished products. FDA also imposes certain requirements that apply to all food, both products for people as well as products for pets:
- Products must be pure and wholesome
- Products must be free of harmful or deleterious substances
- Products must be truthfully labeled
- Canned products must meet the same low acid canning regulations that apply to canned food processed for human consumption
All pet food plants are subject to inspection by FDA and state regulators. Additionally state control officials and FDA have the authority to test pet food ingredients and finished products at any time to confirm they meet the guaranteed nutritional content stated on the label and to verify they are free of undesirable substances. State regulators have the authority to issue a stop sale order in the event they find sufficient cause, such as a failure to meet the nutritional guarantee or due to labeling claims. FDA has the authority to issue a warning to consumers in the event that it concludes that a product on the market is unsafe and should be withdrawn.
Most states require under their state animal feed laws and regulations that pet food labels be registered and approved. Pet food labels are required to provide truthful and non-misleading information, as well as:
- Conspicuously identify the product as a dog or cat food.
- Display the quantity statement and name of manufacturer or distributor.
- Display a brand name that is not misleading as to content or nutritional properties.
- Provide a guaranteed chemical analysis that conforms to state animal feed laws.
- List ingredients in descending order of predominance by weight in the product.
- List ingredients in accordance with AAFCO definitions.
A pet food may not express or imply any claim that a product is complete, perfect, scientific, balanced, etc., under AAFCO regulations, unless:
- It is nutritionally adequate for a normal animal in all of its life stages (growth, adult maintenance, and gestation/lactation), or
- The claim is modified by stating that it is complete and/or balanced for one or more specific life stages.
Pet Food Ingredients
Pet food manufacturers use a wide range of agricultural ingredients. These products include meat, poultry, seafood and feed grains as well as products produced during food processing for human consumption. Ingredients are carefully selected based upon their nutrient profile and their functional contribution to producing products that provide complete nutrition for our companion animals.
Vitamins, minerals and preservatives are added as needed to assure that products provide total nutrition and remain wholesome during distribution and in storage. All ingredients are accepted for use by the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA), the same agencies that regulate human foods. FDA-approved preservatives are used as a safety measure in commercially prepared pet food to help prevent spoilage, which could have adverse health effects on companion animals.
While the majority of ingredients used in pet food are sourced from the United States, the domestic supply of ingredients cannot always meet pet food production requirements, which runs year round so that products are available without interruption. Some ingredients are sourced from outside the United States based on seasonal availability while other ingredients are only available from foreign sources, such as some ingredients essential to producing a complete and balanced pet food like certain vitamins, amino acids, minerals and micronutrients. Interestingly the only significant supply of vitamin C worldwide, which is taken as a daily supplement by people around the globe, is China. Regardless of the country of origin of ingredients, pet food companies take great care to ensure the quality and safety of all the ingredients they use, regardless of source.
Eating High Off the Hog
You may have heard the saying "eating high off the hog." Americans have grown accustomed to doing just that. Yet how many understand the meaning of this saying these days? It refers to the habit of eating what many consider choice cuts of meat, those found to be high on the body of an animal (e.g., shoulders, hams, steaks, roasts and chops). This tendency is different from the past, when it was said that many Americans ate every part of the pig except the squeal.
Over the last few decades most Americans have become very particular about exactly what they'll eat off of animals raised for human consumption. Parts that are nutritious, and not too long ago were viewed as delicious, now are widely shunned. The list includes livers, kidneys, sweatbreads, tripe, chitterlings and feet.
In many places around the globe, these parts of the animal are still considered to be delicacies as illustrated in the list of recipes to the right. In the United States we often refer to these nutritious parts that we choose not to eat as byproducts. In reality they are co-products of the steaks, chicken breasts and hams that we prefer.
Animal co-products are important sources of good quality protein, vitamins, minerals and essential amino and fatty acids for pet food products that do not detract from the human food supply.
In fact cats must have animal proteins or chemically synthesized taurine and arachadonic acid added to their diets as a preventative measure against eye and heart disease because they cannot produce these substances in their body through metabolism.
With respect to food crops, plant co-products similarly are used to make pet food.
No Fillers, Just Function
Making a complete and balanced pet food that provides all the nutrition needed by a cat or dog is a complex task. Veterinarians have identified between 42 and 48 essential nutrients for cats and dogs. Ensuring that a pet food product provides the required nutrition means that three to four dozen ingredients regularly are used. Adding to the complexity of ingredients is the formal process by which these materials are defined.
For 100 years, ingredients used in animal feed, which includes pet food, have been defined by the Association of American Feed Control Officials (AAFCO). AAFCO has developed very specific ingredient definitions that pet food companies must use on their product labels. In addition to describing the source of an ingredient (e.g. beef), often these definitions describe how the ingredient was processed (e.g., boneless, ground and pasteurized).
Pet food makers must use the AAFCO ingredient name on product labels. The result is consistent ingredient labeling requirements across the country and in many cases, the world. It is because of the AAFCO ingredient definition process that the pet food ingredient list includes components names like wheat gluten, poultry by-product meal and sodium selenite.
Pet food ingredients – including those with funny sounding names – all serve at least one specific function in a product whether it be adding nutrients, providing texture, causing the food to hold its shape, preserving freshness, or performing in another capacity. Many ingredients serve multiple functions.
For example, wheat gluten is a relatively expensive ingredient that acts as a binder in pet food products, much like the bread crumbs in a meatloaf. Without wheat gluten, canned products that contain slices, chunks or flakes would not hold their shape. Wheat gluten provides the added benefit of being a source of quality, highly digestible protein.
Often ingredients with funny, chemical sounding names are sources of vitamins, minerals or essential amino acids. Many vitamins, minerals and amino acids are difficult for the body to process in their pure form, so they must be included in food as a compound. Some essential nutrients, like potassium are even deadly in their pure form.
What follows are some examples of sources of vitamins and minerals:
Sodium selenite – Selenium
Pyridoxine hydrochloride – Vitamin B6
Biotin – Vitamin B7
Menadione sodium bisulfite complex – Vitamin K (potassium)
Manganous oxide – Source of manganese
The reason labels list sources of vitamins and minerals in this way goes back to the AAFCO ingredient definition process. AAFCO regulations require that true chemical names be listed on labels.
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.
American Association of Feed Control Officials: www.aafco.org
U.S. Food and Drug Administration: www.fda.gov
Information On Marketing A Pet Food Product: http://www.fda.gov/cvm/consumerpetfood.html
Safe Handling Tips for Pet Foods and Treats Safe Handling Tips for Pet Foods and Treats: http://www.fda.gov/consumer/updates/petfoodtips080307.html
FDA guidance on raw pet food: http://www.fda.gov/bbs/topics/ANSWERS/2002/ANS01183.html
— Audra Avizienis