Dog and Cat Foods
Current regulations require that all labels of pet foods manufactured and sold in the USA must contain the following items: 1) product name, 2) net weight of the product, 3) name and address of the manufacturer, 4) guaranteed analysis, 5) list of ingredients, 6) the words “dog or cat food” (intended animal species), 7) statement of nutritional adequacy, and 8) feeding guidelines. The AAFCO has also adopted an amendment that will require all pet food labels to contain information on the calorie content of the diet, expressed both in kcal ME/kg and per familiar household unit (eg, cups, cans).
The product name is the primary means by which a specific pet food is identified. The way ingredients are listed in the product name may also indicate the percentage of that ingredient present in the product, eg, using the term “beef” in the product name requires that beef ingredients must be at least 70% of the total product or ≥95% of the total weight of all ingredients, excluding water. Using the term “beef dinner,” “beef entree,” or “beef platter,” etc, implies that beef must be at least 10% of the total product, and at least 25% but not more than 95% of the total weight of all ingredients, excluding water. Using the term “with beef” means at least 3% of the total product must be beef, and using the term “beef flavor” implies that there is only enough beef in the product to be detected by taste (<3%).
The product weight must be listed on the front of the pet food label within the bottom third of the principal display panel.
This part of the label lists the minimal amounts of crude protein and crude fat and the maximal amounts of water and crude fiber on an as-fed (not dry-matter) basis. This analysis does not specify the actual amount of protein, fat, water, and fiber in the product. Instead, it indicates the legal minimums of protein and fat and the legal maximums of water and crude fiber content contained in the product. A laboratory proximate analysis lists the actual nutrient concentrations in the food, and two foods that have identical guaranteed analyses may have very different proximate analyses. A guaranteed analysis for protein may list a minimal level of 25%, while the product may (and usually does) contain >25%. A certain variance above or below a minimum or maximum should be expected. Consequently, whenever possible, the manufacturer’s average nutrient profile should be used to evaluate a food.
Direct product comparisons made between like (similar water content) products (ie, dry vs dry, or canned vs canned) are generally valid. However, comparisons across different food types should be made on a dry-matter or caloric basis. As a general rule, dry-food analyses can be converted to a dry-matter basis by simply adding 10% to the as-is value, because most dry foods contain ~10% water (eg, a dry-food protein content of 25% on an as-fed basis is equal to 27.5% dry-matter basis). Canned food analyses can be converted to a dry-matter basis by simply multiplying by 4, because most canned foods contain ~75% water (ie, a canned-food protein content of 6% on an as-fed basis is equal to 24% dry-matter basis). Alternatively, the approximate percent dry matter of a nutrient in a product can be calculated from the information in the guaranteed analysis. First, dry matter in the diet is calculated by subtracting the moisture level from 100%. Next, the percent of the nutrient of interest on a dry-matter basis is calculated using the following equation: (% nutrient [as fed]/% dry matter in diet) × 100 = ~% of nutrient (dry matter).
In the USA, all pet foods sold must be registered with state feed control officials and must contain approved ingredients generally regarded as safe, unless they are for specialized purposes such as the amelioration or prevention of disease. Such foods are considered to be drugs and must be approved by the FDA.
Ingredients are listed in descending order of weight, on an as-fed basis, in the food. Although a food ingredient (eg, chicken) may be listed first, if that ingredient is 75% moisture, it will contribute a much smaller percentage of total nutrients to the food dry matter. In addition, an ingredient such as corn may be listed by individual types, eg, flaked corn, ground corn, screened corn, kibbled corn, etc. In this case, the total corn amount may be a significant amount of the total food dry matter, but when presented as individual types, each type appears lower on the ingredient list. This is referred to as ingredient splitting.
No reference to quality or grade of an ingredient is allowed to be listed; therefore, it is difficult to evaluate a product solely on the basis of the ingredient list. The value of this list is limited to determining the sources of the proteins and carbohydrates for dogs or cats. This kind of information is useful when evaluating animals experiencing an adverse reaction to a food, possibly due to an allergy or intolerance to one or more ingredient sources such as beef, wheat, etc.
Product formulations can be either fixed or open. In a fixed formula, combinations of ingredients and nutrient profiles do not change regardless of fluctuating market prices of the ingredients. In an open formula, ingredients, and possibly actual nutrient profiles, change depending on availability and market prices. Most commercial complete and balanced diets have a fixed formulation.
This statement indicates how the food was tested (feeding versus laboratory analysis or formulation) and for which life stage the food is intended. AAFCO recognizes only four life stages: growth, maintenance, gestation, and lactation. The term “all life stages” is frequently used on a label and indicates that the product has been either formulated or tested for growth. By default, it is anticipated that such a food would also pass a maintenance protocol, because testing a food for growth generally includes gestation and lactation. There are no AAFCO-approved nutrient profiles for geriatric, senior, or weight loss stages.
The statement “complete and balanced” indicates the product contains all nutrients presently known to be required by dogs or cats and that these nutrients are properly balanced to the energy density of the diet. The “complete and balanced” claim must be substantiated by successfully completing AAFCO feeding trials, or the food must contain at least the minimal amount of each nutrient recommended by AAFCO. There are cautions “against the use of these requirements (levels) without demonstration of nutrient availability” because some of the requirements are based on studies in which the nutrients were supplied as purified ingredients and, therefore, are not representative of ingredients used in commercial pet foods. Laboratory analysis does not address the issue of bioavailability. Supplements, snacks, treat products (ie, those intended for intermittent or supplemental feeding), and therapeutic or dietary products (ie, those intended for use under the direction of a veterinarian) are exempted from AAFCO testing.
Commercial dog and cat foods are available in three principal forms: canned, dry, and semimoist. The classifications used depend on the processing method and water content more than on the ingredient content or nutrient profile. Complete and balanced commercial dog and cat diets are formulated to provide adequate quantities of each required nutrient without an intolerable excess of any nutrient. Supplementation of particular nutrients to commercially produced complete and balanced dog and cat foods should be done carefully and only with appropriate justification. Dog foods are not satisfactory for cats because most dog foods are lower in protein, often do not contain assured concentrations of taurine, and are not designed to produce a urinary pH of <6.5 (which helps prevent the crystallization of struvite or magnesium-ammonium-phosphate in the feline urinary tract. (Also see Feline Lower Urinary Tract Disease (FLUTD).)
This is the most popular category of pet food in the USA and some other countries. Dry foods generally contain ~90% dry matter and 10% water. Approximately 95% of dry dog and cat foods are extruded, ie, they are made by combining and cooking ingredients (grains, meat and meat byproducts, fats, minerals, and vitamins), then forcing the mixture through a die. During cooking and extrusion, a temperature of ~150°C (~302°F) converts the starches into a form more easily digested, destroys toxins and inhibitory substances, and flash sterilizes the product. The food is then enrobed with fat and/or digest (material derived from controlled degradation of animal tissues, eg, chicken digest) during drying to increase palatability.
Advantages of dry food include a lower cost than canned or soft-moist food, and refrigeration of unused portions is not needed. Certain types of dry food may also provide beneficial massage of the teeth and gums to help decrease periodontal disease (although unless specifically formulated to deter it, remain mainly ineffective in dogs for this purpose).
Canned dog and cat foods contain 68%–78% water and 22%–32% dry matter. Many of the same ingredients are used in canned pet foods as in dry-extruded types but usually not at the same levels of inclusion. Given their high moisture content, canned foods typically contain higher amounts of fresh or frozen meat, poultry, or fish products and animal byproducts. Many canned pet foods contain textured proteins derived from grains, such as wheat or soy. These materials function as meat analogues, having a physical structure similar to that of meat and high nutritional quality. The use of meat in combination with some of the textured proteins not only controls costs but can improve the overall nutritional profile of the final product.
Canned pet food processing begins with blending meat or meat analogues and fat ingredients with water and dry ingredients, such as vitamins and minerals, for proper nutrient content. The mixture is blended and sometimes ground to produce a fine slurry, depending on product profile. After cans are filled, they are sealed and retorted (a heat and pressure-cooking process that also sterilizes the contents), assuring destruction of foodborne pathogens. Advantages of canned food include a long shelf life in a durable container and high palatability. However, canned food is more expensive than dry food.
Soft-moist dog and cat foods contain 25%–40% water and 60%–75% dry matter. They do not require refrigeration and are preserved using humectants—substances that bind water so that it is unavailable for bacteria and mold growth and assure shelf life. They include simple sugars (usually sucrose), sorbitol, propylene glycol, and salts. Many soft-moist foods are acidified using phosphoric, malic, or hydrochloric acid to further retard spoilage. Advantages of soft-moist foods include convenience, high energy digestibility, and palatability. However, soft-moist food is more expensive than dry food.
Dogs can be successfully maintained on properly formulated home-cooked diets; this is much more difficult in cats. Advantages of home-cooked diets include the use of fresh, high-quality ingredients chosen by the owner. Disadvantages include preparation time, variable quality control and diet consistency, higher cost, and the difficulty in formulating and preparing a nutritionally complete and balanced diet. It is most difficult to formulate a nutritionally complete and balanced diet with sufficient nutrient density in a small volume of food that is palatable for cats. Many home-cooked diets result in foods that are high in protein and caloric density and have inappropriate calcium:phosphorus ratios and inadequate levels of calcium, copper, iodine, fat-soluble vitamins, and several of the B vitamins. Many published recipes for feline diets have very high ash or mineral levels because of the extent of synthetic nutrient supplementation required. If owners choose to feed a home-cooked diet, they should use a recipe formulated by a veterinary nutritionist (vs found on the Internet). It is also important to realize that no home-cooked diets have undergone the testing and research used to formulate complete and balanced commercial pet foods.
Raw meat–based diets have received a lot of attention in recent years. The controversy, lack of good data, and paucity of high-quality research make it difficult for veterinarians to make informed recommendations to pet owners regarding this feeding practice. However, the American Animal Hospital Association, the American Veterinary Medical Association, and the Canadian Veterinary Medicial Association have all developed statements discouraging the feeding of raw or undercooked animal-source protein to dogs and cats. In addition, in 2010, the Delta Society's Pet Partners Program initiated a policy precluding animals eating raw meat–based diets from participating in the Therapy Animal Program.
There are two main types of raw meat–based diets: home-prepared and commercial. In addition, a variety of raw dried or freeze-dried pet treats fall under this category. Home-prepared diets include a variety of feeding regimens, including BARF (Bone and Raw Food or Biologically Appropriate Raw Food), the Ultimate Diet, and the Volhard Diet. Commercial raw meat–based diets most commonly are fresh, frozen, pasteurized, or freeze-dried. Some of these commercial diets are formulated to meet AAFCO nutrient profiles, but many are not.
One of the biggest areas of controversy surrounding these types of diets are the safety of these diets to not only the pets consuming them, but to the pet owners and others who are exposed to the animals consuming them. Even if owners purchase meat meant for human consumption to produce home-prepared diets, there is no assurance these ingredients are free of pathogens and safe to consume uncooked. Raw chicken is a common source of Salmonella, and it is estimated that 21%–44% of chicken purchased from retail locations meant for human consumption throughout North America is contaminated with Salmonella. Even if a pet owner takes precautions while handling and preparing these diets, it has been shown that after consumption of a single meal contaminated with Salmonella, 44% of dogs shed Salmonella in their feces for as long as 7 days, and none of these dogs was symptomatic for Salmonella infection. Salmonella contamination rates for beef and pork intended for human consumption are estimated to range from 3.5%–4%; however, beef and pork are a source of other potential pathogens, including the pathogenic strain of E coli O157:H7. Campylobacter spp is estimated to be present in 29%–74% of chicken, and Listeria spp is estimated to be present in 15%–34% of chicken and 25%–52% of beef and pork. In two separate studies, consumption of raw meat was shown to significantly increase the seroprevalence rate of Toxoplasma gondii in cats.
Some commercial raw meat–based diets are frozen or freeze-dried; however, neither freezing nor freeze-drying destroys all the potential pathogens in these products. Some commercial raw meat–based diet manufacturers now use high-pressure pasteurization in an attempt to reduce the risk of pathogens. Although this process can reduce the numbers of many pathogens, it usually does not completely eliminate them, and bacteria and viruses vary in their susceptibility to this process. Commercial pet foods have also been recalled in recent years because of contamination from Salmonella; however, considering the number of commercially available pet food products, the percentage of products affected is relatively small compared with the number of raw meat–based diets affected.
Another concern, particularly of home-prepared raw meat–based diets, is nutrient imbalances. In a European study that evaluated 95 homemade raw meat–based diets being fed to dogs, 60% had major nutritional imbalances. There have been a number of case reports pertaining to the development of vitamin D–dependent rickets type I and nutritional secondary hyperparathyroidism associated with dogs being fed raw meat–based diets. Other concerns regarding the practice of feeding raw meat and bones to dogs and cats is the risk associated with esophageal and intestinal foreign bodies and perforation. Feeding raw bones has also been associated with slab fractures and other dental problems in dogs.
Proponents of raw diets often cite that raw meat–based diets are the evolutionary diet of dogs and cats and that domestic dogs and cats have never evolved into being able to digest and absorb commercial pet foods. However, a recent report shows that dogs have 36 regions of the genome that differ from that of wolves, and 10 of these regions play a critical role in starch digestion and fat metabolism. Therefore, the genetic makeup of domestic dogs and cats is not the same as that of wolves. Proponents of raw diets also cite that cooking destroys essential enzymes needed for digestion. While a small amount of protein is destroyed during cooking, and enzymes are proteins, there is no evidence that animals or people require these exogenous sources of enzymes. In addition, many of these enzymes are destroyed in the highly acidic environment in the stomach and never reach the small intestines, where most nutrients are absorbed.
Finally, veterinarians must also consider the potential legal implications of recommending raw meat–based diets. While zoonotic risks can be associated with feeding both commercial and home-prepared diets, if a pet owner, for example, develops a Salmonella infection from feeding a contaminated commercial diet, the pet food manufacturer is generally at risk of legal action. However, veterinarians who recommend home-prepared raw meat–based diets are potentially liable if an owner becomes sick from preparing these diets or as a result of pets shedding pathogens in their feces.