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Vegetarian Diet For Dogs
by David A. Dzanis, D.V.M., Ph.D., DACVN
Many Americans enjoy the vegetarian lifestyle today, either for health or ethical reasons. Some people choose to extend this dietary philosophy to their pets as well, which has prompted the marketing of commercial vegetarian dog and cat foods. There is a spectrum of foods and ingredients that may be included or excluded from a "vegetarian" diet, depending on one’s definition. At minimum, it usually means that most meat sources are excluded from the diet (such as beef, pork, lamb, poultry, and sometimes fish). More restricted diets exclude other foods of animal origin, such as egg and dairy products. Perhaps the most extreme example would be a "vegan" diet, where all foods and ingredients of foods, including vitamin and mineral sources, are excluded if they are derived from animals. Provided foods are carefully combined in appropriate proportions, vegetarian or vegan diets for people can be very nutritious and tasty. However, is the same true for dogs and cats?
To help answer that question, one must consider the normal anatomy and physiology of the dog and cat. Both species are in the scientific order Carnivora ("meat- eaters"), although today the domestic dog is considered more as an "omnivore" (animals that eat both animals and plants). Still, just by comparing the dentition of dogs and cats with that of humans and herbivores (plant-eaters, such as cattle and horses), it is readily apparent that their teeth are designed by nature for eating a diet largely comprised of animal tissue. Their short intestinal tracts compared to humans and especially to animals like sheep or horses also indicate that they are not designed to accommodate diets containing large amounts of plant materials. Their nutritional requirements, such as the need for relatively high amounts of protein and calcium, reflect these dietary limitations.
Cats are even more specific in their nutritional needs, emphasizing their status as "true carnivores." For example, cats cannot convert the beta-carotene in plants such as carrots and dark green vegetables into vitamin A. Rather, they require "pre-formed" vitamin A, such as found in liver and fish oils. Cats also need dietary sources of taurine (an amino acid-like nutrient) and arachidonic acid (an essential fatty acid), both of which are found in appreciable levels only in animal tissues. Thus, while both species can eat and utilize some plant-source ingredients (dogs more than cats), they simply are not intended to eat only plants as are other animals such as cattle and sheep.
Why feed a vegetarian diet to pets?
Many people consider their vegetarian diets to be more healthful than the traditional American diet that includes animal-source foods, and some assume the same to be true for dogs and cats. However, the health reasons that people cite as the basis for their own eating habits may not apply where pets are concerned. For example, dogs and cats do not suffer from problems such as high cholesterol or coronary artery disease at anywhere near the incidence as do humans. Thus, reducing intake of saturated fats and cholesterol by cutting meats out of the diet would not be of any real health benefit in pets. Another concern may be about bacterial contamination of the meat ingredients, which could cause disease when consumed by pets. This may be a legitimate concern when eating raw or undercooked meat or poultry, but properly processed dry or canned pet foods pose a far lesser risk of disease transmission than raw fruits and vegetables. Some vegetarian diets for pets are also offered on the premise that they will prevent food allergies. The true incidence of food allergies in pets is relatively low. Regardless, allergies can also be developed against proteins in plants just as easily, so cutting out the meat sources does little to prevent this problem.
Another reason that a pet owner would wish to feed a vegetarian or vegan pet food is because some people may be philosophically opposed to the consumption of products derived from animals, even by their pets. While this is a personal matter that each pet owner must decide for himself or herself, consideration also should be given to the ethical issue of feeding an animal a diet that is against its nature. To be honest, all commercial pet foods are to varying degrees "unnatural" (no company sells raw, whole rodents or small birds as "cat food"). However, eliminating all animal products from the diets of dogs and cats to meet one’s personal philosophy, regardless how well intentioned, may not be the correct choice if it potentially compromises the health of the pet itself. Fortunately, there are many pets besides dogs and cats that would thrive on a completely vegetarian diet (birds, iguanas, rabbits, horses and goats, to name a few).
Potential problems
The nutritional requirements for dogs and cats are very different from those for humans. Thus, a vegetarian diet perfectly suitable in meeting a person’s nutrient needs may be grossly deficient where dogs or cats are concerned. It is possible, but very difficult, to develop such diets for dogs and cats. The Association of American Feed Control Officials (AAFCO), in cooperation with CVM, has developed the AAFCO Dog and Cat Food Nutrient Profiles, which details the known nutritional requirements for these species. Formulating a pet food to meet all these requirements is not a simple task in any case, but becomes extremely difficult when using only ingredients that would meet the definition of a vegetarian diet (especially a vegan diet).
For example, the protein and calcium needs of the dog and cat are much higher than those for humans. These nutrients are most easily provided through animal-derived ingredients. Some plants, such as soy, are high in protein, but the amino acids within the protein are not as balanced as they are for most animal-source ingredients. Dogs and cats also need a dietary source of vitamin B12, a substance not found in most plants. All animals "need" this vitamin, but plant-eating animals such as cattle and sheep can make their own through the action of bacteria in their gastrointestinal tracts, provided there are adequate amounts of the mineral cobalt in the diet (which is found in plants). As mentioned above, the cat has even more unique nutritional requirements that make it harder to get adequate amounts of all required nutrients in the diet without using some animal-source ingredients.
Can’t these nutrients be replaced using synthetic substitutes? Yes, it is theoretically possible to formulate a diet that meets all these specific needs using synthetic additives. However, it becomes more expensive and far less reliable to do it this way. Even when a product is formulated to meet the nutritional needs "on paper," it may not work in the "real" world. For example, plants also contain phytates, substances that bind calcium and trace minerals, lowering their "bioavailability." So, even when minerals are provided at levels that appear adequate, they cannot be properly absorbed and used by the animal. There are adjustments in the AAFCO Dog and Cat Food Nutrient Profiles to account for decreases in bioavailability of nutrients, but these are made on the assumption that both animal and plant-source ingredients are used. It is impossible to tell whether these levels would still be adequate for a completely plant-based diet.
Finally, even the most carefully formulated diet with respect to providing adequate amounts of all essential nutrients is worthless if the dog or cat does not eat it. While dogs certainly enjoy the occasional snack such as a cookie or piece of fruit and cats will chew on grass and other plants, foods without some animal-source ingredients may not be very palatable, so asking dogs and cats to eat only plant-based foods may not be possible in some cases. Even if the cat or dog does eat the vegetarian diet, it still may not be eating enough to meet its nutritional needs.
Vegetarian diet "check list"
Before and after one decides to offer his or her pet a vegetarian diet, several factors should be considered:
1. Why am I choosing to feed this diet? One needs to balance any perceived health benefit against the real potential health risks. The ethical dilemma of the feeding of animal products to animals should be weighed against the moral concerns of feeding a diet that is opposed to that which would be consumed in nature.
2. Does it meet the nutritional needs of the pet? Many homemade diet recipes, including those found in books and magazines, may be seriously incomplete or unbalanced. Testimonials and "success stories" notwithstanding, they have not been shown by scientific testing to meet the nutritional needs of dogs and cats, and should be avoided. For commercial products, reject anything that does not bear an AAFCO nutritional adequacy statement as required for all "complete and balanced" pet foods in the United States. The label may say that the product "is formulated to meet the nutritional levels established by the AAFCO Dog (Cat) Food Nutrient Profiles." However, since palatability and bioavailability of nutrients are big concerns with vegetarian diets, even greater assurance would be had if the product label bears the statement that "Animal feeding tests following AAFCO procedures substantiate that (the product) is complete and balanced."
3. How is it working? After a month or two on the diet, and occasionally thereafter, try to objectively assess the performance of the diet compared to your pet’s previous food. Has it lost or gained weight? How’s the skin and coat? Energy level? Stool volume and consistency? Ask your veterinarian for an examination and professional opinion on your dog’s or cat’s health status.
Summary
The decision to feed a dog or cat a vegetarian diet is not one to be taken lightly. A vegetarian diet with some animal-source ingredients is more likely to meet the needs of the pet, especially for the cat, than a completely vegan diet. In either case, feeding such a diet carries an element of risk to the health of the animal, so the pet owner must consider the possible consequences of choosing these types of diets. If it is later found that a commercial product does not meet the animal’s nutritional needs, it would also be helpful for the pet owner to report that fact to the company and the appropriate regulatory agencies. That way, corrective measures can be taken to ensure that products on the market are nutritionally adequate for the intended species.
I realise that some animals cannot cut out meat from their diets but cats and dogs can providing that you monitor their needs and do the appropriate research. 
