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Pet Food Types

Commercial dog and cat foods are available in three principal forms: canned, dry, and semi-moist. 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. 

Dry Food:

This is the most popular category of pet food in the UK 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 by-products, 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 Food:

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 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.

Home-cooked Diets:

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:

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.

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