Nutrition myths (Proceedings)


MYTH: Meat by-products are inferior in quality compared to whole meat in a diet.

MYTH: Meat by-products are inferior in quality compared to whole meat in a diet...

When listed on an ingredient label, meat is defined by the AAFCO as any combination of skeletal striated muscle or that muscle found in the tongue, diaphragm, heart, esophagus with or without the accompanying and overlying fat and the portions of the skin, sinew, nerve and blood vessels which normally accompany the muscle derived from part of whole carcasses. It also must be suitable for use in animal foods. This excludes feathers, heads, feet and entrails. Meat by-products are defined as non-rendered, clean parts of the carcass which may contain lungs, spleen, kidneys, brain, liver, blood, bone, heads, feet (of poultry), partially defatted fatty tissue, stomach and intestines emptied of their contents. It does not include hair, horns, teeth or hooves. Depending on the supplier and the type of refining process that the manufacturer uses, by-products can vary greatly in the amount of non-digestible material they contain. The ash content can give you an idea of the quality of the by-products. High ash content is an indicator of a poorer quality protein with lesser digestibility. The presence of by-products does not indicate a poor quality diet, a higher ash to protein ratio would. Feeding trials evaluating nutrient content and digestibility will help greatly in evaluating the quality of the ingredients. This information is available in most product reference guides, on-line references and by contacting the manufacturer. Knowing the reputation of the manufacturer is your best indicator of a good quality diet.

MYTH: Feeding trials are not necessary...

Feeding trial protocol as established by the AAFCO for adult maintenance lasts 6 months, requires only 8 animals per group and monitors a limited number of parameters. These parameters are set at the minimum nutrient requirements as defined by the National Research Council. These levels tend to be lower than the recommended daily intake (RDI). Requirements are the minimum level of a nutrient, which over time, is sufficient to maintain the desired physiological functions of the animals in the population. RDI is the level of intake of a nutrient that appears to be adequate to meet known nutritional needs of practically all healthy individuals. The National Research Council recommendations are to serve as a guide to diet formulations, but they do not account for digestibility or nutrient availability. AAFCO feeding trials provide reasonable assurance of nutrient availability and sufficient palatability to ensure acceptability. They also provide some assurance that the product will support certain functions such as gestation, lactation and growth. A feeding trial is also the only way to accurately access the quality of the protein in a diet, as this is the only valid way to determine digestibility of a protein, and therefore its quality. Passing a feeding trial does not ensure that the food will be effective in preventing long-term nutrition/health problems or detect problems with a low prevalence in the general population. A feeding trial is also not designed to ensure optimal growth or maximize physical activity. If a diet has not gone through a feeding trial by the manufacturer, you will be conducting the feeding trial for them using your patients and pets. While feeding trials especially on therapeutic diets cannot be expected to detect all deficiencies or excesses (which may also be due to malabsorption or maldigestion) they give you an added advantage of having someone else evaluate them before you offer them to your clients. Feeding trials are conducted on healthy dogs and cats, with controls that are the same breed and gender. During the trials, the animals must receive the test food as their only source of nutrition. The same formula must be fed throughout the entire trial. The trials are conducted by measuring the daily food consumption, weekly body weight measurement, stated lab parameters measured at the end of the trial, complete physical exam by a veterinarian at the beginning and end of the trial, a number of animals, not to exceed 25% can be removed for non-nutritional reasons or poor food intake, necropsy conducted on any animal which dies during the trial with findings recorded, reproducing animals need the additional following information recorded, body weight within 24 hours of delivery, offspring's body weight within 24 hours of birth, litter size at birth, 1 day later and at end of study, any stillborn or congenital abnormalities.

At the end of the feeding trial, the results obtained are compared to the results from a control group, a historical colony average or to reference values published by the AAFCO.

All premium manufacturers conduct feeding trials on their foods, and continue to conduct them as the foods are changed and updated both for palatability and as new evidence is discovered regarding nutritional requirements. To verify if feeding trails have been conducted on a food, check the product label to find the source of AAFCO certification, if feeding trials have been done, it will be stated on the label as such.

MYTH: Pet food preservatives are bad...

Preservatives are defined as any substance that is capable of inhibiting or retarding the growth of microorganisms or of masking the evidence of such deterioration. The primary nutrient requiring protection from preservatives during storage is dietary fat. These fats can be in the form of vegetable oils, animal fats or the fat-soluble vitamins A, D, E and K. These nutrients have the potential to undergo oxidative destruction, called lipid peroxidation, during storage. Antioxidants are included in foods to prevent this lipid peroxidation. Oxidation of fats in pet foods also result in loss of calorie content and the formation of toxic forms of peroxides that can be harmful to the health of pets. The FDA defines an antioxidant as any substance that aids in the preservation of foods by retarding deterioration, rancidity or discoloration as the result of oxidation processes. Various types of antioxidants have been accepted for use in human and animal foods since 1947. Antioxidants do not reverse the oxidative effects on foods once they have started, but rather retard the oxidative process and prevent destruction of the fats in the food. Because of this, antioxidants to be fully effective must be included in the food when it is initially mixed and processed. This inclusion helps prevent rancidity, maintaining the food's flavor, odor, and texture and prevents accumulation of the toxic end products of lipid degradation.

Antioxidants can be divided into two basic types-natural derived products and synthetic products. Natural-derived products are commonly found in certain grains, vegetable oils and some herbs and spices. While these products do exist in nature, all of these compounds are processed in some way to make them available for use in commercial foods. The most common natural derived antioxidants include mixed tocophrols (vitamin E compounds), ascorbic acid (vitamin C), rosemary extract and citric acid.

Alpha tocopherol has the strongest biologic function on tissues, but is a poor antioxidant in foods. Delta and gamma tocopherols both have low biologic activity but are more effective than alpha tocopherol as antioxidants. Tocopherols used in foods are obtained primarily from distillation of soybean oil residue. Tocopherols are rapidly decomposed as they protect the fat from oxidation, for this reason food preserved with mixed tocopherols have a shorter shelf life than food preserved with a mixture of antioxidants.

Ascorbic acid (vitamin C) is a water soluble antioxidant and is not easily soluble with the fatty portion of foods. It does work synergistically with other antioxidants, such as vitamin E and butylated hydroxytoluene. Ascorbyl palminate is similar in structure to ascorbic acid, though it is not normally found in nature, when hydrolyzed it yields ascorbic acid and the free fatty acid (FFA) palmitic acid, both of which are natural compounds.

Rosemary extract is obtained from the dried leaves of the evergreen shrub, Rosemarinus officinalis. It is effective as a natural-derived preservative in high-fat diets and has been shown to enhance antioxidant efficiency when combined with mixed tocopherols, ascorbic acid and citric acid. Much processing of the plant oil is needed before addition to foods due to the taste associated with the oil affecting the taste of the food.

Citric acid is found in citrus fruits such as oranges and lemons, and is often included in combination with other natural-derived antioxidants.

Due to the high cost of using these compounds they are usually used in conjunction with synthetic antioxidants as preservatives in pet foods. It is difficult to attain the necessary level of natural derived antioxidants without becoming cost prohibitive.

Synthetic antioxidants are more effective than natural-derived antioxidants and better withstand the heat, pressure and moisture during food processing, this is called "carry through". By being more effective they better preserve the fat-soluble vitamins A, D and E for activity in the body rather than in the food.

Synthetic antioxidants include butlyated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tertiary butylhydroquine (TBHQ) and ethoxyquin. BHA and BHT are approved for use in both human and animal foods and have a synergistic antioxidant effect when used together. BHA and BHT also have good carry-through and a high efficiency in protection of animals fats, but are slightly less effective when used with vegetable oils. TBHQ is an effective antioxidant for most fats and is approved for use in human and animal foods in the United States but is not approved for use in Canada, Japan or the European Economic Community, so it is not usually used in pet foods in the international market. Ethoxyquin has been approved for use in animal feeds for more than 30 years, and has been used in pet food manufacturing for more than 15 years. It is approved for both human and animal foods, has good carry-through and has especially high efficacy in the protection of fats in foods. Ethoxyquin is more efficient as an antioxidant than BHA or BHT, which allows lower levels to be used. It is especially effective in protection of oils that contain high levels of polyunsaturated fatty acids (PUFA).

If the use of synthetic antioxidants has clients concerned, they should be made aware that most canned foods do not contain antioxidants, and that many commercially prepared dry foods use natural derived antioxidants. There are no studies that support the contention that synthetic antioxidants in general or Ethoxyquin in particular are responsible for the variety of health problems reported by owners to the FDA. The proper use of antioxidants prevents the occurrence of rancidity and the production of toxic peroxide compounds in foods. In most cases, synthetic antioxidants are the best choice because of their efficacy, good carry-through and cost. In contrast, poor carry-through, instability and high levels needed for effective protection make natural-derived antioxidants difficult to use as the sole source in pet foods.

MYTH: All foods are created equally

Food quality cannot be determined by the label, the commercial or the celebrity endorsement. When trying to compare two different foods whether they are canned, dry or somewhere in between, comparing products using metabolizable energy (ME) gives a better idea of caloric distribution, and allows you to accurately compare dissimilar diets. ME does not take into account digestibility of the diet in the animal, this can only be determined through the use of feeding trials.

To determine ME:

Total calories in 100 grams of food

      Protein grams × 3.5 kcal/gram = protein kilocalories in food

      Fat grams × 8.5 kcal/gram = fats kilocalories in food

      Carbohydrate grams × 3.5 kcal/gram = carbohydrate kilocalories in food

Total calories/100 gram = protein calorie + fat calorie + carbohydrate calorie

Percentage of ME contributed by each nutrient (caloric distribution)

Protein = (protein calories/100 gram ÷ by total calories/100 gram) × 100 = % ME

Fat = (fat calories/100 gram ÷ by total calories/100 gram) × 100 = % ME

Carbohydrate = (carbohydrate calories/100 gram ÷ by total calories) × 100 = % ME

If the grams of nutrients/100 gram of food is not given, than using the guaranteed analysis and kilocalories/100 grams the following formula can be used. Because you are not accounting for metabolic or fecal/urine losses, these values are not as accurate as the metabolizable energy values.

Energy Density from Guaranteed Analysis

% in diet of nutrient × modified Atwater factor = kcal/100 gm of food

Divided % nutrient by total calories to get nutrient distribution

Modified Atwater factors are the amounts of energy/gram of nutrient

Protein and carbohydrates are 3.5, fats are 8.5

If the kilocalories/100grams is not given, a rough estimate of the ME can be determined from the Guaranteed Analysis. This is also called a "proximate analysis" and is the same as "percent as fed".

% in diet of protein × 3.5 = protein/100 grams of food

% in diet of fat × 8.5 = fat/100 grams of food

To find carbohydrates: (100 %-( % protein- % fat- % crude fiber- % moisture- % ash)) × 3.5 = carbohydrate/100 grams of food.

Add these three numbers together to get an estimate of total calories/100 grams. Calculate percent ME as above.

As with human grade foods and products, the same factory can produce multiple foods of varying quality. Factories may also produce food for multiple pet food manufacturers. The manufacturer does not necessarily determine the quality of the food any more than a parts manufacturer for a car determines the quality of the final product. It is also important when comparing foods to see if feeding trials have been done on the product and look at digestibility, if given. If you chose a food that has not had feeding trials done by the manufacturer, than you are doing the feeding trials for them.


Once clients are given the facts regarding pet foods, all our jobs should become easier! After all, a well informed client is our best friend. With proper information, they will be able to pick a pet food that contains quality ingredients, have undergone feeding trials and are properly preserved to that all the ingredients are available to their pet. They may also learn that their veterinary team is the best source for nutrition information!


Case LP, Carey DP, Hirakawa DA, Daristotle L. Digestion and Absorption, Nutrient Content of Pet Foods: in Canine and Feline Nutrition 2nd Edition. Mosby , St Louis 2000. pp 60-63, 175-185

Hand MS, Thatcher CD, Remillard RL, Roudebush P. Nutrients, Making Commercial Pet Foods, Making Pet Foods at Home: in Small Animal Clinical Nutrition 4th

Edition. Mark Morris Institute, Topeka 2000. pp 58-60, 140-146, 167-169

Wortinger, A. Nutrition Myths. Nutrition for Veterinary Technicians and Nurses. Wiley-Blackwell. Ames 2007. pp 205-210

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