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By Jean Hofve, DVM
Commercial food is a great convenience to dog and cat guardians. Responsible consumers who want the best for their animal companions have a bewildering array of foods and claims to choose from. How do you know what's best for your animals? The most reputable manufacturers of "superpremium" and "natural" foods agree with holistic veterinarians that the very best diet for your animal companion is one that you make yourself. A homemade diet, carefully balanced nutritionally and using raw and organic foods, is closest to what Mother Nature intended. (For a sample homemade diet, click here.) However, many of us do not have the time or energy to do home cooking, especially for multiple animals or large dogs. So, for those of us who rely, partially or entirely, on commercial foods for our animals, here are some guidelines to use in selecting a good-quality diet. Content The name of a pet food is strictly defined and tells us what is actually in the food. "Chicken for Dogs" must contain at least 95% chicken (excluding water). Similarly, "Fish and Giblets for Cats" will be 95% fish and giblets together, and there must be more fish than giblets, since fish appears first on the label. If the label says "dinner," "platter," "entree," "nuggets," "formula," or similar term, there must be 25% of the named ingredients. That is, "Fish Dinner" must contain 25% fish. If more than one ingredient is named, such as "Fish and Giblets Entree," the two together must comprise 25% of the total, and the second ingredient must be at least 3%. Ingredients labeled as "with" must be present at 3%, such as "Fish Dinner with Giblets." An ingredient labeled as a "flavor," such as "Beef Flavor Dinner," may not actually contain beef meat, but more likely will contain beef digest or other beef by-products that give the food a beef flavor. 
By-Products Even on premium brands, you will notice one of the major ingredients listed is "by-products" of some sort. By-products are basically defined as "parts other than meat." These may include internal organs not commonly eaten by humans, such as lungs, spleens, and intestines, other parts such as cow udders and uteri, and in the case of poultry by-products, heads, beaks and feet. By-products must be from "freshly slaughtered" animals, although there is some question as to how fresh they really are by the time they reach the pet food manufacturer. Rendered Products Rendering (basically a process of slow cooking) produces two major items: animal fat or tallow, and a processed product usually called "meat meal," "meat and bone meal," or "by-product meal." (Due to historical quirks in naming, the term "by-product meal" refers to poultry, while the equivalent mammalian product is called "meat and bone meal.") Animals that are dead, dying, diseased, or disabled prior to reaching the slaughterhouse are known as "downers" or "4D" animals. These are usually condemned, in whole or in part, for human consumption, and are generally sent for rendering along with other by-products, parts and items that are unwanted or unsuitable for human use - such as out-of-date supermarket meats (along with their plastic wrappers), cut-away cancerous tissue, and fetal tissue (which is very high in hormones). Rendered ingredients vary greatly in quality. A few rendering facilities are closely associated with slaughterhouses, which are in turn connected with feedlots or poultry farms. These "captive" rendering plants are more likely to produce good quality, relatively pure meals. Such meals are typically designated with the name of the source animal, such as "chicken meal." Because of the way they are processed, dry foods must use meals as their major animal-source ingredients. Meals do contain higher proportions of protein than meat, since the fat and water have been removed. A few dry foods advertise that they contain some type of "meat" (such as chicken or beef) as the first or a top ingredient. However, because of the high water content of fresh meat, the actual percentage is small. The first named meal is usually the primary protein source in these foods. Many independent renderers accept for processing such items as road kill, euthanized shelter dogs and cats, and other unappetizing ingredients. These items are not supposed to find their way into the pet food chain but are theoretically converted for use in fertilizers, livestock feeds, and industrial applications. Over the years there have been numerous unsubstantiated reports of this material being processed into dog and cat food. The Center for Veterinary Medicine, a branch of the Food and Drug Administration, admits that dead dogs and cats are commonly rendered, and although there is no legal prohibition against using dogs and cats in pet food, they do not "condone" the practice. All the large, reputable pet food manufacturers certify that they do not use such materials in their products. "Complete and Balanced" A food may be labeled as "complete and balanced" if it meets the standards set by a group called AAFCO, the American Association of Feed Control Officials. These standards were formulated in the early 1990s by panels of canine and feline nutrition experts. Standards set by AAFCO have been adopted by most states, which are then responsible for enforcement. However, in many cases, state enforcement is negligible. A food may be certified by AAFCO in two ways: (1) meeting published standards for content, or (2) feeding trials. (1) Nutrient Profiles. These standards set the required amounts of protein, fat, vitamins, minerals, and so forth. These theoretically have the benefit of extensive research behind them. However, according to researchers at the University of California at Davis, the fundamental research supporting standards for adult cat food includes one study on protein requirements, one study on amino acid requirements, and ZERO studies on vitamin requirements. Yet AAFCO publishes standards specifying exactly how much of each vitamin must be included in adult cat food. Where do these values come from? They are interpreted and extrapolated from research in kittens (which has been a little more extensive) and from research in other species, mostly chickens and rats. Is this valid? We do not know. Moreover, any manufacturer can synthesize a food containing sufficient amounts of each ingredient according to the standards, yet an animal will ultimately starve to death on it. How could this happen? Because the standards do not address the issues of "bioavailability" of nutrients to the animal. Certain forms of vitamins and minerals, for example, are poorly absorbed from the digestive tract. A noted veterinary nutrition textbook claims that a food can be created from old leather boots, wood shavings, and crankcase oil that will meet the technical requirements for protein, carbohydrates, and fats, yet would be completely indigestible. Unfortunately, given the ingredients used by some manufacturers, "Old Boot" may be closer to the truth than anyone wants to admit! (2) Feeding Trials. These are considered the "gold standard" of pet food formulation. However, when you look at the actual AAFCO protocols for an adult maintenance diet, a manufacturer must feed exclusively the test food to only six animals for six months. (Eight animals are required at the outset; however, two of them may be dropped from the trial for non-diet-related reasons.) Foods intended for growth and reproduction must be tested for only 10 weeks. Most of the large, reputable pet food producers, such as Iams, Hills, Walthams and Purina, maintain large colonies of dogs and cats, and test their foods on hundreds of animals over years or even multiple generations. Other manufacturers rely on facilities that keep animals for this purpose to do the studies for them. It is easy to see how a poor quality diet could be fed for only six months without seeing adverse health effects, and legitimately be labeled as meeting AAFCO standards. In fact, studies have confirmed that even foods that pass feeding trials may still be inadequate for long-term maintenance. Keep in mind, too, that the standards, such as they are, set only "minimums" and "maximums," not "optimums." Commercial foods are designed to be adequate for the average animal, but may not be suitable for an individual animal's variable needs. 
Additives and Preservatives Virtually every commercial pet food contains additives and preservatives. Some of the worst include BHA, BHT and ethoxyquin. Monsanto, manufacturer of ethoxyquin (a rubber stabilizer), in 1993 was ordered to conduct a new study of this preservative due to faulty test protocols and alleged doctoring of data in its initial report. Not surprisingly, the second study, completed in 1996, found no problems associated with ethoxyquin in pet food. Given Monsanto's track record, do you believe this? Ethoxyquin is banned from nearly all human food products (except certain spices) due to its cancer-causing properties. Contaminants Another concern is pesticide residues, antibiotics, and molds contained in pet food ingredients. Meat from downer animals may be loaded with drugs, some of which are known to pass unchanged through all the processing done to create a finished pet food. One toddler who habitually snacked from the cat's bowl of dry food died of an allergic reaction to penicillin, which was found to be in the cat food at levels over 600 times that allowed in human food products. In the 1990s there were two major recalls of dry dog food by different manufacturers due to mold contamination of grain ingredients. Some fungal toxins are very dangerous. The second recalled food killed more than 20 dogs. In 2006, more than 100 dogs died from another food contaminated with a fungal toxin.
What to do? When selecting a commercial food for your animal companion, be sure to read the label. Although percentages are misleading due to the variable moisture content of processed foods, they are the only data available. Avoid foods containing "by-product meal," "meat and bone meal," or the newest euphemism, "beef and bone meal," which tend to be the least expensive (and thus potentially poorest quality) animal-source ingredients. "Meat and bone meal" (MBM) is the mammal equivalent to "by-product meal" (which is properly applied only to poultry). MBM was reported as the ingredient most likely to contain the drug used for euthanasia (sodium pentobarbital) in a study conducted by the FDA. .
A named meat or meat meal should be the primary protein source, rather than a cereal like corn gluten meal. Corn in all its forms must also be avoided. Corn has the same glycemic index as a chocolate bar, and is probably the primary culprit in the development of feline diabetes. Corn gluten meal, a high-protein corn extract, is often substituted for more expensive meat ingredients. Its presence in a food indicates a company's preference for economy over nutritional value. Wheat is also a common allergen; wheat products should be avoided. Both grains are susceptible to mold and other toxins.
Because the pet food makers have gotten pretty clever about marketing, it's important to know how to see through the hype. For instance, don't fall for the "meat is the first ingredient" ploy! For more about pet food marketing, see this article.
Never feed "semi-moist" type foods, which are full of colorings, texturizers, and preservatives. Avoid foods containing chemical preservatives such as ethoxyquin, BHA, BHT, propylene glycol, or propyl gallate. In general, select brands promoted to be "natural." While they are not perfect, they are better than most. Many brands are now preserved with Vitamins C and E instead of chemical preservatives. While synthetic preservatives may still be present, the amounts will be less.
Stay away from "light" or "senior" or "special formula" foods. These foods may contain acidifying agents, excessive fiber, and inadequate fats that will result in skin and coat problems. Avoid generic or store brands; these may be repackaged rejects from the big manufactures, and certainly contain cheaper - and consequently poorer quality - ingredients.
Change brands or flavors of dry food every 2 or 3 months to avoid deficiencies or excesses of ingredients, which may be problematic for your animal. (With canned food, you can change flavors daily if you wish--my cats prefer it that way!) Whenever you are changing foods, remember to GO SLOWLY. Add a tiny amount of new food to old, and gradually increase the proportion of new food. It will take a week or two to properly transition a cat. Click here for more info on why and how to change foods.
Cats need at least 50% of their diet (preferably 100%!) in the form of wet food (canned or homemade), for optimal health. Include a variety of meats and flavors to prevent finicky behavior and food allergies and intolerances. Cats who are overweight, diabetic, or have a history of or current liver, pancreas, bladder or kidney disease, should not eat any dry or semi-moist food at all. The low moisture and high carbohydrate content are known to contribute to these problems. There is no real benefit to the cat from dry food, and many adverse effects on health. Dry food is popular because of its cost and convenience, but it is definitely not healthy for your cat to eat. (And no, dry food does not clean the teeth!)
If you must feed dry food, remember to never get it wet. Do not mix with canned food, milk, broth, or water. All dry foods have bacterial contamination on the surface, and moisture will allow those bacteria to grow. Some are dangerous and cause vomiting and/or diarhhea. Above all, supplement with organic raw meats (meat should be frozen at -4F for 72 hours, then thawed prior to use; follow safe meat-handling procedures at all times) and lightly steamed, pureed or finely grated vegetables (they cannot be very well digested by carnivores otherwise). Dogs may be supplemented with tofu and cooked grains; however, cats should receive minimal carbohydrates in the diet. Be aware that plant products tend to raise urine pH and may contribute to urinary tract disease. Other helpful supplements include Omega-3 fatty acids, acidophilus, digestive enzymes, and Vitamins C and E. There are many excellent books, articles, and websites available for more detailed guidelines on ingredients, proportions, and preparations.
For a more detailed look at diet and nutrition in cats, including Dr. Jean's list of "approved" commercial foods by brand name, see "What Cats Should Eat" in our Bookstore. For more great articles on important feline health and behavior topics, visit our Publications Page.
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