Wednesday, April 8, 2009

Pet Nutrition: Requirements and related diseases Part 4 Pet Food Labels and Product Types

While American Feed Control Officials (AAFCO) and the National Research Council (NRC) cooperate to publish dog and cat nutrient profiles for growth, maintenance, and reproduction, this series goes beyond the percentages suggested by these organizations and explores in more detail why nutrients are required and what happens if they are not supplied in sufficient quantities. In part 1 we discussed water and energy, in part 2 we talked about protein, fats, carbohydrates and fiber and in part 3 we looked at vitamins and minerals. Today we are going to broaden our discussion by talking about various pet food product types available to us and pet food labeling requirements and issues.

Manufacturers of all commercial dog and cat foods are legally required to provide certain information on the label, including name of product, guaranteed analysis, ingredient guarantee, net weight, and name and address of the manufacturer or distributor. The most important nutritional information on the label is the guaranteed analysis, ingredient list, and the statement of nutritional adequacy. 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.

Guaranteed Analysis:
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 2 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 rule of thumb, 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).
Ingredient List:
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. 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 that are having an adverse reaction to a food, possibly due to an allergy or intolerance to one or more ingredient sources such as beef, poultry, rice, corn, 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.

Statement of Nutritional Adequacy:
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 4 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 3 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.

Dry Food:
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. About 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 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. Dry food may also provide beneficial massage of the teeth and gums to help decrease periodontal disease.

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 analogs having a physical structure similar to meat and high nutritional quality. The use of meat in combination with some of the textured proteins not only holds costs down but can improve the overall nutritional profile of the final product.
Canned pet food processing begins with blending meat or meat analogs 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 food borne 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. Reports of an increased risk of Heinz body anemia in cats that consume soft-moist foods preserved with propylene glycol have raised concerns over the use of propylene glycol in cat foods, and it has been removed from the generally recognized as safe list for cat foods. 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 due to the extent of synthetic nutrient supplementation required.
Stay tuned for part 5 disussing feeding practices at the various life stages of an animal.
Notes: Contribution
Merck Veterinarian Manual

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