Timely Topics in Nutrition Nutritional Adequacy of Diets Formulated for Companion Animals
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0901TTN.QXD 10/12/2005 2:20 PM Page 601 Timely Topics in Nutrition Nutritional adequacy of diets formulated for companion animals Erin L. Steiff, MS, and John E. Bauer, DVM, PhD, DACVN be studied at the molecular level, and today these tech- The JAVMA welcomes contributions to this feature. niques are being applied to determine genetic compo- Articles submitted for publication will be fully reviewed nents of those diseases. Modern scientific inquiry and with the American College of Veterinary Nutrition (ACVN) acting in an advisory capacity to the editors. Inquiries exploration will continue to provide information con- should be sent to Dr. John E. Bauer, Department of Small cerning the 2 recognized forces of nature and nurture. Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station, TX Use of Dogs in Nutritional Research 77843-4474. Throughout the course of our scientific advance- ments, dogs have remained faithful companions. Many early and current discoveries were made because of ogs and humans share a unique relationship that 4 Dhas existed throughout the world for centuries. dogs. For example, one of the early studies conducted The evolutionary nature of this relationship and infor- in dogs found that the B vitamin niacin was a treatment for pellagra. Also, in the 1920s, investigators conduct- mation about the early days of domestication are 5 unknown. However, one may assume that some efforts ed historic studies that involved the use of dogs to were made by humans to feed their canine compan- document the relationship of insulin and diabetes mel- ions, and symbiotic relationships developed. As litus. Although our understanding of human nutrition domestication emerged, humans continued to share has been advanced as a result of responsible scientific food with dogs, even though it was unknown how the investigations that involved dogs, those studies have food nourished and sustained them. Cats, which were provided information on more than human nutrition. domesticated more recently than dogs, also have a Advances in nutrition and feeding of dogs, per se, have unique history, but their story is even more uncertain.1 also relied on this information and have provided the basis for the formulation and production of wholesome The Scientific Method dietary products for exclusive preparations for dogs. As The scientific method was born during the interest in human health has continued to expand, Renaissance as humans began to increasingly question demand for high-quality nutritional products for com- the world around them. The advent of the germ theory panion animals has also expanded. Companion animal of disease elicited great excitement, because it seemed nutritionists and veterinarians have responded by that every disease could be explained on the basis of working together to develop a wide array of foods to causative agents. However, a few diseases defied this provide complete and balanced diets for many needs. theory. For example, scurvy was the first disorder to be In recent years, improvements in foods formulated for linked with diet rather than a bacterial agent. Beri-beri, companion animals have resulted in many premium pellagra, and rickets soon were added to the list.2,3 For pet food products. Despite these developments, some the first time, the groundwork was laid for the identi- pet owners prefer formulating food at home for their fication of relationships between diet and certain dis- animals. Reasons for this include the belief that home- eases, which led to the discovery of essential vitamins. prepared diets are less expensive, more nutritious, or Certain essential nutrients could be used to treat com- bring them closer to their pet; however, many of these panion animals and humans afflicted by recognized reasons are anecdotal. Although owners generally have disorders attributable to lack of specific nutrients, and good intentions, many lack the scientific knowledge or a new era of nutritional discovery had begun. other resources necessary to address important nutri- During the 20th century, another category of dis- tional needs of their pets. Thus, the potential exists for eases began to appear. Heart attacks, hypertension, and home-prepared diets to cause nutrient deficiencies, diabetes seemed to be linked with excesses of nutri- excesses, or imbalances. ents, rather than deficiencies. Advances in scientific techniques allowed various aspects of these diseases to Determining Food Composition From the Comparative Nutrition Laboratory, Department of Small An important part of determining a diet’s nutri- Animal Medicine and Surgery, College of Veterinary Medicine, tional adequacy involves determining food composi- Texas A&M University, College Station, TX 77843-4474. tion. A widely used method for determining food com- Address correspondence to Dr. Bauer. position is proximate analysis.6 This technique JAVMA, Vol 219, No. 5, September 1, 2001 Vet Med Today: Timely Topics in Nutrition 601 0901TTN.QXD 10/12/2005 2:20 PM Page 602 involves separating the food into 6 fractions: moisture, digestible energy. After absorption, macronutrients are ash, crude protein, ether extract, crude fiber, and nitro- metabolized, and fat and carbohydrate are oxidized. gen-free extract (NFE). Moisture content is deter- Oxidation of protein is not as efficient as that for fat or mined by desiccating the food, usually at 100 C, and carbohydrate, and some energy is lost via the urine in measuring weight loss. Ash is obtained by heating the the form of protein compounds. Thus, the actual ener- food at 550 C to remove all of the carbon, hydrogen, gy available for metabolism is known as metabolizable and oxygen; the remaining ash contains the minerals energy (ME).9 For dogs, fat contains approximately 8.5 and other inorganic substances. Crude protein is deter- kcal of ME/g, and protein and carbohydrate contain 3.5 mined by calculation after quantifying the amount of kcal of ME/g. A food formulated for dogs will typically nitrogen in a sample of the diet. It should be men- have 3.5 kcal of ME/g of dry-matter content, but some tioned that not all of the crude protein is available for diets may contain more than this amount.8 Dry matter use by an animal. Some of the nitrogen in the assay consists of all nonwater nutrients (macronutrients, vi- may have come from nonprotein sources. Also, protein tamins, and minerals). digestibility may limit the amount available to an ani- Energy (ie, calories) is utilized in an animal’s body mal, and some proteins and formulations may be less to support 4 unique needs: basal metabolism, expendi- digestible than others. Ether extract is obtained by ture of heat increment, activity, and production (eg, mixing the food with a lipid solvent, and this fraction growth, gestation, or lactation). Basal metabolism is is further used to quantify dietary lipid content. the internal work of the body when at rest in a nonfed Although several methods for determining the various state.9 For example, ion transport is an important part types of fiber exist, detailed summaries of these tech- of basal metabolism for which energy is used. niques7 are beyond the scope of this article. It is suffi- Expenditure of heat increment is the additional energy cient to state that this fraction is commonly deter- expended in the postabsorptive state that is released as mined as crude fiber, which slightly underestimates heat. Activity denotes muscular contraction or other fermentable fiber content. Total dietary fiber also can work. Productive expenditure of energy refers to be determined, and this method is used for measuring growth in a young animal or pregnancy, lactation, or fiber in foods formulated for humans.7 Finally, remain- muscle accretion in a mature animal. The energy ing components are the nonprotein extractives, often requirements of an animal change as these factors vary. referred to as NFE, which contain nonfiber carbohy- Thus, the energy requirement of dogs varies with size, drates. The NFE is determined by subtracting the other stage of life, activity, environment (thermoregulation), 5 components (expressed in units of grams per kilo- neutering status, and health status (ie, disease state).7 gram of food) from a value of 1,000 g.6 Home-prepared diets often contain excess energy. Pet owners may be tempted to provide a pet with too Evaluation of Nutritional Adequacy much food because they fear it will be hungry. Other of a Diet owners may substitute excess food for personal atten- After determining food composition, evaluation of tion. Furthermore, calories in home-prepared diets are the nutritional adequacy of a diet and its particular not as easily calculated as those in commercial foods blend of nutrients is performed. One method is to com- because of variability of ingredients or recipes. Thus, pare the amount of each important nutrient contained over-consumption of energy will lead to obesity when in the diet with the amount recommended for that not balanced by an increase in activity. Obese dogs are nutrient. Another approach commonly used by manu- prone to osteoarthritis, respiratory distress, cardiac and facturers is to follow feeding protocols established by circulatory problems, diabetes mellitus, liver problems, the Association of American Feed Control Officials and immune deficiencies.10-12 (AAFCO), a regulating body of the pet food industry.8 These procedures are useful, because they provide for Protein—Protein provides 2 essential nutrients the actual feeding of animals during a particular stage (essential amino acids and nitrogen used to make other of life, which allows for direct assessment of the diet in nitrogen-containing compounds). There are 10 essen- question. There are many ways in which a diet would tial amino acids recognized for dogs, and these same 10 be unsuitable if not formulated with care. For example, plus taurine are needed by cats13; some authors also a diet may be unsuitable because of excess, deficiency, recognize 2 to 3 semi-essential amino acids.