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Preparation with Food Safety

Pet Food Contamination
Food is unsafe when it is contaminated with potentially pathogenic microorganisms. Vigilance to prevent feeding such food begins with procurement and is essential throughout preparation and storage. Toxic chemicals also make food unsafe to eat. They can be produced by microorganisms before or after procurement and many cannot be removed or destroyed by cooking. Some chemicals not considered toxic are used in processed foods to improve appearance, physical qualities or shelf life. Some animals react to these food additives. Food safety is concerned with preventing clinical signs of illness cause by pathogens, toxins and additives. Discussions on bacterial and toxin contamination in commercial pet food are found in Commercial Pet Food Contamination in the appendix.

Pet Food Additives

Pet foods are like all processed foods in that they contain ingredients with no nutritional value. These additives improve a product’s appearance or stability. Emulsifiers and surface-active agents keep water and fat from separating. Antioxidants are added to prevent fats from oxidizing, or become rancid. Antimicrobial agents reduce spoilage. Added flavors and color improve a product's acceptability by owners and their pets. Some additives are nutrients that the animal absorbs and metabolizes. Examples include sorbitol and ethylene glycol which retard spoilage. These additives can produce diarrhea. Others such as ethylene glycol can cause anemia in cats.

Most pet food additives are not inert. The intestine digests and absorbs many, such as sucrose and ethylene glycol. Bacteria metabolize many others in the large intestine. The chemical products formed can damage the intestinal mucosa to cause colitis and possibly cancer. The intestine absorbs some of these chemicals and they can cause disease in other parts of the body.

Some pet foods prepared especially for animals with certain diseases claim to contain no additives. They contain none of the chemicals that a pet food label must list. They can contain others that do not require documentation on the label; some can cause problems. For example, dogs can be treated for chronic diarrhea by feeding a lamb and rice diet. The owner prepares this diet and when it is effective the pet has normal bowel movements. The owner may eventually choose to feed a commercially prepared lamb and rice diet. Sometimes this pet food causes the diarrhea to recur, showing that this therapeutic diet contains more than lamb and rice. One or more unstated additives must be responsible for the pet food's failure to achieve the results of the owner-prepared diet.

Most animals remain healthy when fed pet foods containing additives. Consequences of their long-term consumption are unknown. For most healthy pets additive-free foods are not any better, or worse, than foods containing additives. Proponents of the use of additives claim that " of foods on the basis that they contain no additives or are 'all natural', is a marketing gimmick only designed to increase sales."1 On the other hand the use of additives are also gimmicks to increase sales (using artificial color and flavors) or to maintain sales (using preservatives) of a product. Preservatives allow a product to sit on a shelf for months before it is fed. One's knowledge of any additives in an owner-prepared diet will always be greater than the information one can have on any commercially prepared pet food. The public learns far more about the composition and safety of an owner-prepared diet's ingredients (almost entirely foods designed for human consumption) than any commercial pet food.

Commercial pet foods contain many additives for improving product appearance and stability.2 Additives are not used for nutritional value. Emulsifiers and surface-acting agents are used to prevent separation of fat from water. Added antioxidants prevent fats from becoming rancid and antimicrobials reduce spoilage. Added flavors and color improve acceptability.

Additives in processed foods

Anticaking agents

Flavoring agents, adjuncts

pH control agents

Antimicrobial agents

Flour-treating agents

Processing aids


Formulation aids


Colors, coloring adjuncts


Solvents, vehicles

Curing agents

Leavening agents

Stabilizers, thickeners

Drying agents


Surface-active agents


Nonnutritive sweeteners

Surface-finishing agents

Firming agents

Nutritive sweeteners


Flavor enhancers

Oxidizing and reducing agents



Antioxidants are important additives in processed foods for both human and pet consumption.3 They are added to retard the oxidation of fats. Animal, fish, and especially plant fats attract oxygen, resulting in their oxidation. This chemical reaction results in rancidity, destruction of vitamins, and produces dangerous chemicals, peroxides. These chemicals can cause disease. Antioxidants effectively and safely slow fat oxidation and peroxide formation.

Naturally occurring antioxidants such as vitamin E and vitamin C (also others such as rosemary leaves) are effective in extending shelf life for many processed foods. Natural antioxidants are more costly and larger amounts are needed compared to chemicals like ethoxyquin. Reduction of fat oxidation consumes naturally occurring antioxidants. Consumption of vitamins to slow rancidity can result in their deficiency. Because vitamin E is unstable, (in retarding rancidity; processing of pet foods also degrades it), a more stable form is used (encapsulated acetate ester). Thus, commercial vitamin E added to pet food may not improve stability by reducing oxidation. Ethoxyquin added to pet food spares other antioxidants, and by that minimizes vitamin deficiency. Rancidity is less likely in comparison with using naturally-occurring antioxidants.

Some question the need for antioxidants in pet foods. A human food such as potato chips fried in fat without any antioxidant is edible for only six days. It is edible ten times longer when an antioxidant is added. Antioxidants are most important when pet foods contain fats high in unsaturated fatty acids. A pet food with fish oil or vegetable oil as an important source of fat becomes rancid rapidly when no antioxidants are added. Peroxide levels can increase 12 times within 24 hours when such foods contain no antioxidants. Rancidity can reduce a food’s metabolizable energy by 15 to 20 percent. Commercial pet foods processing can significantly accelerate oxidation. Antioxidants are by definition a feed additive, but they are essential for preventing oxidation and preserving a food’s nutritional content and quality.

In the 1960s some cat foods were made with fish meal and fish oil without any antioxidants. These diets caused steatitis, a serious and sometimes fatal problem. Adding antioxidants to cat food solved the problem.

Pet foods contain ethoxyquin and a few other commercially prepared antioxidants because they are relatively low-cost and are not consumed as they retard rancidity. Ethoxyquin is safe as well as effective. There is more than three-quarters of a century of study of this chemical. Like almost any chemical if a dog or cat receives enough, it can be toxic. Ethoxyquin has a very wide range of safety, however, and the amount added to pet food causes no problems. Its permitted use as a preservative is 0.015 percent, which is a very low concentration.

Ethoxyquin, more so than any other antioxidants, has anticancer properties. It interferes with cancer induction by other chemicals through actions not dependent on being an antioxidant. Ethoxyquin can bind carcinogenic chemicals and to enzymes that convert inert chemicals into ones causing cancer.

Other Chemical Preservatives
Many other chemical preservatives prolong shelf life for pet foods. Some of these are found in the following table. Ascorbic acid and its salts are preservatives. Butylated hydroxyanisole and butylated hydroxytoluene retard rancidity. (They are the most common antioxidants in processed foods for human consumption.) For most other antioxidants there is little information on any being toxic. An exception is the potential toxic effect of nitrite. Nitrite is used in meat for human consumption and bacteria can change the chemical to another form with carcinogenic properties, nitrosamines. Very small amounts of this chemical also cause acute and chronic liver damage.

Chemical preservatives

Ascorbic acid/ascorbate salt


Sodium sulfite

Benzoic acid/benzoate salt

Potassium/sodium bisulfite

Sorbic acid/salt

Butylated hydroxyanisole

Propionic acid/propionate salt

Sulfur dioxide

Citric acid

Propyl gallate

Tertiary butyl hydroquinone

Erythorbic acid

Resin guaiac

Thiodipropionic acid


Sodium nitrite


Common preservatives to prevent yeast growth in sugars are sorbic acid and potassium sorbate. Hydrochloric or phosphoric acid is added to make the product slightly acid which reduces bacterial growth and spoilage. These products generally contain high amounts of coloring matter; red coloring is added to simulate meat and white (titanium dioxide) to simulate fat. The final product looks like meat and fat.

Additional Special Purpose Products

Many substances are available for purposes listed in the table shown here.

Special Purpose Ingredients



Aluminum sulfate

Anti-gelling agent

Attapulgite clay

Anti-caking agent

Ball clay

Pelleting agent

Calcium stearate

Anti-caking agent

Diatomaceous earth

Inert carrier

Disodium EDTA


Ethyl cellulose

Binder or filler

Ethoxylated fats


Guar gum


Iron ammonium citrate

Anti-caking agent


Anti-caking agent

Locust bean gum


Mineral oil


Monosodium glutamate


Phosphoric acid




Propylene glycol




Saccharin sodium




Tetra sodium phosphate


Most of the materials or chemicals are inert and cause no problems. Others can be toxic at levels much higher than usually found in processed foods. It is apparent that most of the substances control the physical characteristics, i.e., appearance, of pet foods. Thus, these substances are rarely found in diets prepared by a pet owner. AAFCO (1995) is the source for this list.

The list here is only partial. Many other materials are found in pet foods and some can cause problems. Carrageenan, an example of such an ingredient made from seaweed, is a carbohydrate that can cause intestinal inflammation. Some pet foods contain carrageenan to produce a desired physical quality. Some pets react to commercial pet foods with persistent digestive tract disturbances. It is possible that carrageenan in some pet foods is responsible for inducing inflammation resulting in digestive tract disease.

Unique Feline Food and Additive Intolerances
Cats are more sensitive to food additives than other animals. Cats are intolerant to the common food preservative, benzoic acid. Benzoic acid occurs naturally in plants but is not found in animal tissues. Cats have a limited ability to metabolize the chemical to a form that the body can excrete. Aspirin is a form of benzoic acid that cats excrete poorly.

Cat foods can contain propylene glycol which can damage erythrocytes. The result is a shorter life span that can lead to anemia.

Relatively small amounts of onions can poison cats. Documented cases appeared after eating onion soup and baby foods containing onion as a flavoring agent.

Cocoa and chocolate can poison dogs and the toxic derivative, theobromine, can be lethal for cats.

Cats may have other unique intolerances that are currently unknown. Feline hyperthyroidism has been associated with feeding commercial canned cat food. This disease may be related to cats' unique needs that are not being met or to some food additives.

Pet Food Preparation

Food selection is the essential first step in practicing food safety. Food handling and preparation procedures determines that the final diet is safe for consumption. Owners control food safety when they prepare diets themselves. They have no control over the safety of any commercially prepared or process foods.

The U. S. Department of Agriculture Food Safety and Inspection Service (FSIS) has established a farm-to-table approach to improve the safety of meat and poultry at each step in the food production, distribution, and marketing chain. After the consumer purchases these foods the FSIS gives a number of reasons for handling food safely.4 Most importantly safe food handling prevents illness and can save a pet’s life. Owners preparing a pet’s diet have a responsibility to the animal to handle food safely and this also saves money. Safe food handling is easy and its practices are the ones most likely to preserve food’s peak quality. Growth of microorganisms is reduced and quality of food appearance, flavor, and texture is maintained. Nutritional benefits are not lost and food need not be discarded because of decay or temperature abuse.

Safe handling of food by consumers begins in the store and continues in the home. The important practices of handling include purchasing, storing, pre-preparation, cooking, serving, and handling leftovers. Safe handling prevents or minimizes hazards that consist of biological (bacteria), chemical (cleaning agents), and physical (equipment).

Meat and poultry products should be purchased last during shopping and packages of raw meat and poultry should be kept separate from other foods, especially ones eaten without further cooking. Plastic bags should be used to enclose individual packages of meat.

Home storage of meat should be in a refrigerator at temperatures below 40o F or in a freezer at a temperature of 0o F. Most foodborne bacteria grow slowly at 40o F and do not grow at 0o F. Meat is refrigerated or frozen immediately at home. Juices from raw meat are not permitted to drip on other refrigerated foods. Hands are washed with soap and water for 20 seconds before and after handling any raw meat, poultry or seafood product. According to CDC, hand washing is the single most important means of preventing the spread of infection from bacteria, pathogens and viruses causing disease and foodborne illness. Canned foods are stored in a cool, clean dry place, avoiding extreme cold or heat. Foods should not be stored under a sink or directly on the floor; they should be stored separate from any cleaning supplies.

Pre-preparation most importantly includes handwashing done before and after food handling. It is essential after touching animals or blowing the nose that interrupts the handling. Juices from raw meats should not contaminate other foods that will not be cooked before eaten. In addition to hand washing, counters equipment utensils, and cutting boards can be sanitized with a chlorine solution of one teaspoon liquid household bleach per quart of water. Frozen foods are never thawed at room temperature; thawing is done in the refrigerator. Foods can be thawed in the microwave if the product is cooked immediately. Thawing can also be done in cold water in an airtight plastic wrapper or bag, changing the water every 30 minutes until thawed.

Food is always cooked thoroughly which destroys any pathogenic bacteria. Freezing or rinsing food in cold water is unacceptable for destroying bacteria. Beef products are cooked to at least 160o F to destroy E. Coli and other pathogenic bacteria. Poultry and pork products are heated to at least 170o F to destroy Salmonella and other pathogens. It may be safest to heat to 180o F. (As an example, bringing to a boil and simmering chicken thighs for one hour is more than enough to kill all bacteria.) A meat thermometer can be used to verify that this temperature is reached. Meat products are cooked thoroughly the first time and then they may be refrigerated and safely reheated later. Never cook them partially to complete cooking later. Never refrigerate partially cook products. Microwaving foods are done following the manufacturers instructions and using microwave-safe containers and procedures to assure thorough cooking.

Food is handled for serving only after hands are washed with soap and water. Food is served in clean dishes or containers. Foods are not allowed to stand for appreciable lengths of time between 40o F and 140o F, a temperature zone in which bacteria multiply rapidly. This time should not exceed two hours at room temperature and a maximum of one hour on hot days at 90o F.

Leftovers can be handled before and after handwashing. Clean utensils and dishes are used. Leftovers are divided into small units and stored in shallow utensils for quick cooling. They should be refrigerated within two hours of cooking. Foods left out too long are discarded. Leftovers are reheated thoroughly to a temperature of 165o F or until hot and steamy. If there is any question of the safety of leftovers they should be discarded.


Government and industry call for pet food ingredients to be "wholesome." The definition of wholesome is "good for one's health" or "healthful." Foods with predictably high levels of microorganisms or toxins can produce signs of gastrointestinal disease and cannot be considered wholesome. They should not be used to produce food for pets.

Bacteria live in the small intestine and they represent the retention of orally ingested bacteria.5 The kinds and numbers of bacteria living there change as the population of ingested bacteria change. Bacteria are contaminants of food and/or environment. The contamination of the small intestine can be controlled by using wholesome foods and proper processing for producing pet foods. Recent studies show that the bacterial population of the small intestine can be reduced slightly by the addition of some novel complex nondigestible carbohydrates to pet food.6 Use of such substances to prevent the consequences of bacterial contamination of pet foods should not replace efforts to produce a product by using wholesome ingredients.

In summary commercial pet foods contain many additives. Some must be listed on the label. Many others need not be listed. Food additives can cause health problems. Very few are proven to cause problems, however. For many of the others it is difficult to prove any harmful effects. No doubt, some of these chemicals can interact with others to synergistically damage cells in different parts of the body.

Medical problems sometimes disappear when pets are fed an owner-prepared diet but return when the same ingredients used in these diets are fed in the form of a specially prepared commercial pet food. In such cases a pet food additive can be be responsible for the health problem.

Many substances are available for purposes listed here. Most of the materials or chemicals are inert and cause no problems. Others can be toxic at levels much higher than usually found in processed foods. It is apparent that most of the substances control the physical characteristics, i.e., appearance, of pet foods. The list here is only partial. Many other materials are found in pet foods and some can cause problems. Carrageenan, an example of such an ingredient made from seaweed, is a carbohydrate that can cause intestinal inflammation. Some pet foods contain carrageenan to produce a desired physical quality. Some pets react to commercial pet foods with persistent digestive tract disturbances. It is possible that carrageenan in some pet foods is responsible for inducing inflammation resulting in digestive tract disease.


1. Lewis, Lon D., Mark L. Morris, Jr., and Michael S. Hand. 1987. Small Animal Clinical Nutrition III, 3d ed. Topeka: Mark Morris Associates.

2. AAFCO (1995) Official Publication of the Association of American Feed Control Officials Inc., Atlanta, GA.

3. Hilton JW: 1989. Antioxidants: function, types and necessity of inclusion in pet foods. Canadian Veterinary Journal 30:682-684.

4. Anonymous. 1997. Food Safety and Inspection Service. U.S. Department of Agriculture, Washington, D.C. (Internet).

5. Willard, M. D., R. B. Simpson, T. W. Fossum, N. D. Cohen, E. K. Delles, D. L. Kolp, D. P. Carey, and G. A. Reinhart. 1994. Characterization of naturally developing small intestinal bacterial overgrowth in 16 German Shepherd Dogs. Journal American Veterinary Medicine Association 204:1201-1206.

6. Willard, M. D., R. B. Simpson, K. Delles, N. D. Cohen, T. W. Fossum, E. D. L. Kolp, and G. A. Reinhart. 1994. Effects of dietary supplementation of fructo-oligosaccharides on small intestinal bacterial overgrowth in dogs. American Journal Veterinary Research 55:654-659.