INTRODUCTION

There is a growing segment of pet owners that are electing to prepare home made foods for their pets. Their reasons for doing so are diverse. Some owners object to commercial pet food, usually based on perceived fallacies about the ingredients, quality or processing of pet foods. Others simply believe that preparing home made diets is healthier, more natural or they can use ingredients that are natural, organic, vegetarian, vegan, or consistent with their moral or ethical beliefs. Some people believe that preparing the pet's diet strengthens the human-companion bond. There is also a misconception that it is cheaper to home prepare the pet food rather than purchase a commercial product. Home made diets require considerable time, effort and expense.

In general, veterinary nutritionists agree that healthy pets should be fed a complete and balanced, commercially prepared food. Unlike commercially available foods, home made diets have not been adequately tested with animal feeding trials or laboratory analysis to confirm nutrient content and nutrient availability. Furthermore, owners are likely to substitute different ingredients without understanding the full ramifications involved. Ingredient substitution or deletion is likely to unbalance the diet. Home-made diets are often crudely balanced and may not achieve satisfactory palatability, digestibility or safety. A study by Roudebush et al reported that 90% of home made diets used for managing adverse food reactions were not nutritionally adequate.

The primary indication for a home made diet is the patient with medical problems that simply can not appropriately be managed with a commercial product. The type of disease may range from an adverse reaction to food (food hypersensitivity) to a combination of medical problems. For example, a patient with a problem list of chronic pancreatitis, chronic renal insufficiency, hypertriglyceridemia and calcium oxalate urolithiasis. It is clear that the nutritional management of such a patient is indeed difficult, and there is not yet a single commercial diet that can appropriately manage this particular combination. Home made diets can provide adequate nutrition and assist the management of disease processes provided that a properly formulated diet is used, the correct ingredients are included and the recipe is strictly adhered to.

Formulation

Formulating a home prepared diet requires a complete understanding of the nutrient requirements of the pet, and the effect of the disease process on the nutritional requirements. Detailed nutrient analyses of the ingredients selected and a thorough knowledge of dietary interactions are needed. Finally knowledge of the effect that preparation and storage has on nutrient availability is necessary. Home-made diet recipes can be obtained from the veterinary literature, textbooks and the internet. However, caution should be applied when retrieving recipes from the internet or lay publications. These recipes should be scrutinized to ensure that they are indeed complete and balanced for the pet, or that they have the appropriate nutritional modifications to indeed help assist the management of a disease process. Consulting with a board certified veterinary nutritionist is the best option to obtain a diet specifically designed for each pet requiring a home made diet.

Diets can be formulated using hand calculation, computer-assisted calculations, or commercially developed computer software programs. These tools are used to alter the ratio's of the ingredients selected for the home made diet until the nutrient analysis profile is consistent with that which is required by the pet. The biggest limitation of these techniques is providing accurate nutrient profile information on the ingredients. Two resources for obtaining nutrient profile details on ingredients are the USDA handbook 8 and Bowes and Church's Food Values of Portions Commonly Used. Ingredient selection should be based on nutrient content, availability and cost.

The recommended nutrient requirements for healthy pets can be obtained from the National Research Council of the National Academies--Nutrient Requirements of Dogs and Cats, or from the Official Publication of the Association of American Feed Control Officials (AFFCO). The NRC recommendations are generally obtained studies using purified diets. AAFCO recommendations are based on NRC requirements, but include safety factors to account for variability in the ingredients, the effect of manufacturing etc.

The first step in formulating a home made diet is to calculate the energy requirements of patient. Direct measurement of a patient's energy consumption is not readily available. Consequently, several equations have been recommended to estimate the requirement. These equations utilize the resting energy requirements (RER), basal energy requirements (BER), or maintenance energy requirements (MER). Basal energy requirements describe the energy that is needed to meet the needs of cells and organs under a stress-free, thermoneutral environment, and in a post-absorptive state. The resting energy requirements (RER) accounts for the energy required by the animal in a resting state, and includes physiologic influences and the assimilation of nutrients. The RER can be calculated as 70 x BW (kg)^0.75kcal/day. The maintenance energy requirements (MER) encompass all the energy required for maintaining normal body condition in a normal pet. The MER for dogs = 110 x BW(kg)^0.75kcal/day, and for cats is 60 x BW(kg) kcal/day. The MER may need to be adjusted according to the age and life-style of the patient such as growth, pregnancy or lactation. It should be remembered that the MER provides only a good starting point. Actually caloric requirements can vary by as much as 25%, hence adjustments in daily caloric intake may need to be made to maintain the pet in ideal body weight and body condition score.

The daily energy requirement can be achieved using a combination of protein, fat and carbohydrate. Fat is a concentrated source of energy, supplying 2.25 times more energy per unit volume than carbohydrate or protein. Fat can contribute to the palatability of the diet for dogs. Unless there is a specific contraindication such as pancreatitis, lymphangiectasia or gastrointestinal disease, the fat can be added to achieve between 20-40% of the calories. The essential fatty linoleic acid can be supplied in vegetable oils such as soybean oil. Fish oils can be used to provide long chain omega-3 fatty acids. Cats have an absolute requirement for arachidonic acid, which must be supplied from animal fat.

The next step is to determine the protein intake of the pet, and to select the primary source of protein for the diet. AAFCO recommends a minimal crude protein intake of 51.4 g/1000 kcal for adult dogs, and 65 g/1000 kcal for adult cats. Protein sources that can be utilized include eggs, cottage cheese, meat, poultry, fish, and cereals such as soybean (tofu). Animal proteins are more likely to reflect amino acid profile necessary for dogs and cats. Cereal proteins are often deficient in key amino acids such as methionine, tryptophan or lysine. Once the crude protein requirement met, the recipe should be further evaluated to ensure that the minimal requirements for essential amino acids are achieved. Liver is often used as a protein source in diets, and it is exceptionally palatable for dogs and cats. However, high concentrations of liver should be avoided in home made diets because of the risk of vitamin A toxicity with long term or exclusive feeding.

Carbohydrates are used to supply the balance of the energy requirements and to provide a source of fiber. Sources of carbohydrates include corn, rice, wheat, potato, barley, tapioca and pasta. In general, the ratio of carbohydrate to protein should be at least 1:1. Fiber sources included canned pumpkin, wheat bran, oat fiber and Metamucil.

Once the main protein, fat and carbohydrate ingredients have been selected, the vitamin and mineral content of the diet must be evaluated. With respect to calcium and phosphate, both the absolute amounts of both minerals and the ratio of calcium to phosphate are important. Correction of calcium and phosphate deficiencies may be achieved using calcium carbonate, dicalcium phosphate or steamed bone meal. Steamed bone meal is rather high in sodium hence it may need to be avoided in patients with diseases associated with sodium retention and hypertension. Depending on the main ingredients selected, sodium and/or potassium supplementation may be necessary. These can be supplied as table salt (sodium chloride), lite salt (combination of sodium chloride and potassium chloride) or salt substitute (potassium chloride). The remaining vitamins and minerals can be balanced using a multi-vitamin and mineral supplement. There are a variety of vitamin and mineral supplements available. Many that are marketed for dogs and cats are not complete and balanced, nor have bioavailability studies been performed. When looking at human preparations, liquid vitamin and mineral supplements seem appealing, but these are typically deficient in folic acid which is not compatible in solution with riboflavin.

Once the recipe has been finalized, the owner must be provided with very specific instructions on the preparation, storage and feeding of the diet. The owner should purchase a kitchen scale, measuring spoons and cups to accurately weight out the quantity of ingredients. The carbohydrates should be cooked separately from the meat source. Cooking improves the digestibility of the carbohydrate source and destroys any antinutritional factors such as trypsin inhibitors. Meats, fish or poultry must be properly cooked for at least 10 minutes at 180°F or 80°C. Following cooking the ingredients (except the vitamin and mineral supplement) should be thoroughly mixed or even blended using a food processor. The diet should be stored in air tight contains in the refrigerator for no longer than 3-5 days. Alternatively, the diet can be frozen and thawed immediately prior to use. The diet should be warmed to body temperature prior to feeding to the pet. The vitamin and mineral supplement should not be blended or stored with the diet as they are easily destroyed.

Errors

The most common errors with home made diets include excessive quantities of protein, and the formulation of diets that are deficient calories, calcium, vitamins and microminerals. High quantities of meat, coupled with calcium deficiency result in abnormal calcium to phosphate ratios. Nutritional secondary hyperparathyroidism manifesting as bone pain and osteopenia may occur. Diets formulated for cats are often deficient in fat and have a low energy density. Attention must also be given to the nutrition peculiarities of cats. Cats have evolved as true carnivores, and as such, can not obtain all necessary nutrients solely from plants or plant products. Consumption of animal products is essential for taurine, arachidonic acid and vitamin A.

Owner related errors typically revolve around ingredient substitution, elimination of the vitamin and mineral supplement, and feed raw meats and bones. Ingredient substitution and elimination can arise because of the inconvenience to obtain the ingredients, the expense of the ingredients or from failure to understand the importance of strictly adhering to the recipe.

Raw meat and eggs may contain bacteria, parasites, and viruses. Studies have suggested that 20-35% of raw poultry carcasses test positive for Salmonella, and 80% of raw food diets for dogs tested positive for Salmonella. Furthermore, 30% of stool samples from dogs were positive. Salmonella outbreaks have been reported in dogs receiving raw meat diets. Raw meats have also tested positive for E.coli, and Yersinia enterocolitica. Parasites that can be present in raw meat include Toxoplasma gondii, Sarcocystis, Neospora caninum, Toxocara canis, Trichinella spiralis, Taenia and Echinococcus. In addition to placing the pet at risk, people may also become infected after handling raw contaminated meat intended for dogs and preparing raw food diets. Therefore it is important to stress the need for hygiene when preparing foods, and for complete cooking of the raw ingredients.

Monitoring

Routine monitoring of the pet that is fed a home made diet is important to ensure that the diet optimizes the health of the pet. At each visit, the client should be asked to describe how much and how they are preparing the diet to verify compliance with the original recipe. The daily caloric intake and appetite of the pet should be recorded. The body weight, body condition score, hair and skin coat condition are good indicators of the nutritional status of the pet.

References

1.  Dobenecker B, Kienzle E. Development in computer aided diet calculation for dogs and cats. Proc The Waltham International Science Symposium, Bangkok, Thailand, 2003, p 59

2.  Joffe DJ, Schlesinger DP. Preliminary assessment of the risk of Salmonella infection in dogs fed raw chicken diets. Can Vet J 2002;43:441-442

3.  LeJeune JT, Hancock DD. Public health concerns associated with feeding raw meat diets to dogs. J Am Vet Med Assoc 2001;19(9):1222-1225

4.  Freeman LM, Michel KE. Evaluation of raw food diets for dogs. J Am Vet Med Assoc 2001:218(5): 705-709

5.  Steiff EL, Bauer JE. Nutritional Adequacy Of Diets Formulated For Companion Animals. J Am Vet Med Assoc 2001;219[5]:601-604.

6.  The Animal Nutritionist, N-Squared Computing and Durango Software, Silverton, OR

7.  Pennington JAT. Bowes & Church's Food Values of Portions Commonly Used. JB Lippincott, Philadelphia, PA

8.  USDA Nutrient Database for Standard Reference, http://www.na l.usda.gov/fn ic/foodcomp/

9.  Zootrition-Dietary Management Software: www.zootrition.org