Introduction
The use of alternatives to traditional commercially available diets for dogs (such as home cooked or raw diets) is an emerging issue in veterinary medicine. This is due in part to consumer distrust of commercially manufactured diets, secondary to several recent food recalls, and to the perception of commercial diets as unhealthy and low quality by some sectors of the population. Certainly this perception has been promoted and exploited by various dog care publications, websites and other information sources for dog owners, including marketing materials from manufacturers of 'niche' commercial dog foods. However, no feeding approach is without potential pitfalls, and it is important to assess the risks and benefits of alternative feeding regimes in dogs with the help of currently available scientific evidence. Veterinarians can benefit from understanding these issues in order to confidently discuss and counsel owners regarding the appropriate diet for a particular animal.
Home Cooked Diets
There are several reasons why many pet owners prefer feeding a home cooked diet to a healthy pet in the United States. Some people may consider home cooked diets more natural and healthful, especially in light of recent pet food recalls. They may want to avoid ingredients that they perceive as unhealthy or inadequate (such as preservatives, color additives, grains or by-products) or may want to include specific ingredients (organic ingredients, vegetables, specific meats). Other people want to feed their dogs according to their personal beliefs (such as vegetarianism or veganism). Additionally, some pets will not readily consume commercial diets, either as a result of a learned behavior or due to food aversions. Finally, some owners simply enjoy cooking for their dogs.
For dogs that have a disease process, their owners may want to participate in the management of their pet by preparing its diet at home, which gives a sense of control over the disease. The relationship of nutrition to health is a generally accepted idea. In some disease processes, the role of nutrition is clearer than in others. There are nutritional recommendations out there for almost any disease process, both for humans and for animals. In animals with a disease amenable to nutritional management, home cooking is indicated if the pet will not eat an adequate commercial diet. In some cases where co-morbidities are present, home cooking is the only option (such as in dogs with renal disease and concurrent pancreatitis).
Benefits
Benefits of home cooked diets include palatability, high digestibility, and ability to control exactly the ingredients and/or nutrient levels of the diet. The biggest advantage of these diets is the fact that they can be custom made for a particular animal: with ingredients known to be palatable, providing the necessary calories for that particular pet, and including any modifications that are needed if there is a disease process present. Many of these advantages are lost when generic recipes (from the Internet or from books) are used. These recipes are not custom-made for the individual animal, are generally vague and/or complex, and many contain potentially problematic ingredients (such as bone meal, onions and garlic). Vague ingredients include "ground beef" (unspecified fat content), "cooked chicken" (unspecified cut and method of cooking), and "multivitamin". There are many multivitamins marketed for either humans or pets that vary widely in their nutrient content. Pet multivitamins are generally formulated to be safe when added on top of commercial diets, so the levels of potentially toxic nutrients (such as zinc, vitamin A, and vitamin D among others) are not provided in appropriate proportions and amount to be adequate for balancing a home cooked diet. Generic published recipes are often outdated, since the knowledge regarding nutrient requirements and nutritional management of diseases is constantly evolving.
Disadvantages
The main caveats to home prepared diets are the expense (both in time and money), "diet drift" (substitutions or elimination of ingredients over time), and the impossibility of performing feeding tests to ensure nutritional adequacy. Properly balanced home cooked diets are formulated by computer using a database of ingredients to be adequate according to the minimum requirements of dogs as published by the NRC in 2006 and yearly by the Association of American Feed Control Officials (AAFCO). Due to individual variation in energy and essential nutrient requirements and the variation attributable to ingredients it is possible that a generic diet recipe would not be adequate for a specific animal. Commercial canine and feline diets that undergo AAFCO-regulated animal feeding tests have been fed to dogs or cats (the number of animals, the duration of the trial, and the variables measured are all defined in the AAFCO manual) and thus ensuring the digestibility and bioavailability of the nutrients. Obviously, it is impossible to assess every custom home cooked diet recipe with feeding trials. These trials are our best tool to ensure nutritional adequacy, although they are not perfect, in the sense that long-term or subtle deficiencies or toxicities may not be detected. The reason that not all commercial diets undergo these tests is mainly due to their cost. Some pet food manufacturers, especially smaller companies, are unable or unwilling to invest in feeding trials to help ensure appropriate digestibility and bioavailability of their foods. The trials are especially important in diets for animals subject to high nutritional demands, such as gestation, lactation, and growth.
The Nutrition Support Service at UC Davis analyzes many home cooked diet recipes by computer to assess for adequacy. Deficiencies frequently seen in these recipes are linoleic acid, calcium, trace minerals, choline and many other vitamins. In some cases, toxic levels of vitamins A and D have been observed. One study published in the early nineties (Roudebush and Cowell, 1992) evaluated via a computer program 116 home cooked recipes recommended by veterinarians and 90% were not nutritionally adequate for adult maintenance according to the current recommendations at that time.
Recipe Assessment and Monitoring
Evaluation of the diet by a veterinary nutritionist is recommended, but an initial assessment can be made by any veterinarian. To do so, a complete diet history is very important. A protein and fat source should be identified (many diets are deficient in the essential fatty acid linoleic acid, especially those using lean meats such as chicken breast as the main ingredient). A calcium source should be identified, bearing in mind that calcium requirement of dogs and cats are considerably higher than those of humans. A source of taurine (for cats and some particular dog breeds, or dogs with certain medical conditions) and a source (or several) for essential vitamins and minerals should also be present. Cats, as obligate carnivores, need several nutrients only present in animal tissues, such as retinol, cholecalciferol, taurine, and niacin (Morris, 2002). A more quantitative analysis to establish the nutritional adequacy of a home cooked diet requires time and adequate computer software.
For animals that eat home cooked diets, consultation with a veterinary nutritionist is recommended and frequent rechecks are recommended (2-3 times a year), including body weight, physical exam, blood work, and urinalysis; in order to monitor for any nutrient deficiencies or excesses that may occur. Examples of clinical manifestations of nutrient deficiencies or toxicities include nutritional secondary hyperparathyroidism, rickets, skin disease, hypercalcemia, and anemia. A diet history should be taken at every visit to ensure that recommendations are still adequate (nutritional recommendations frequently change over time and with changes in the patient's condition) and that there has been no diet drift. Home cooking is a viable option for many pets, and many owners are very capable of doing this safely, but proper formulation and frequent monitoring is very important.
Raw Food Diets
Raw diets are touted by proponents to have many health benefits, and are claimed to be a more species-specific type of diet for dogs (and also cats). The thought process behind these statements is that dogs are carnivores and evolved eating raw food, and that heat processing of foods destroys nutrients and enzymes necessary for their assimilation.
There is a lack of scientific evidence to support any health benefit of feeding raw diets compared to commercial diets or to home cooked diets. However, there are many websites that provide testimonials and success stories of animals fed raw diets as evidence of their superiority to home cooked diets or to commercially available diets.
There are three main types of raw diets: home prepared, such as recommended by Dr. Billinghurst (BARF; Bones and Raw Food diet or Biologically Appropriate Raw Food diet); commercially available (usually sold frozen); and combination diets (a "premix" can be bought to be mixed with a raw meat). Commercially available raw foods are regulated just like any other pet food, by state laws, AAFCO, and the FDA. The FDA statement on raw foods can be found here: http://www.fda.gov/cvm/Guidance/Guide122.pdf. Adherence to these particular guidelines is voluntary.
The major issues related to the feeding of both home prepared and commercially available raw diets to dogs are nutritional adequacy, potential adverse effects of feeding bones, and pathogenic contamination.
One of the concerns regarding raw food diets is their nutritional adequacy. Home prepared raw food diets have the same problems as home cooked diets: they are often unbalanced, they can be vague in instruction, and they can drift. Also, they have not been tested to ensure adequate bioavailability of the nutrients. Many of these diets rely on bones to provide enough calcium to the animal, and the bioavailability of calcium from bone can vary depending on different factors.
Freeman and Michel (2001) published a paper assessing nutritional adequacy of 3 home prepared and 2 commercial raw food canine diets. Samples of these diets were analyzed in the laboratory and the results were compared to AAFCO minimum requirements. Some of the nutritional problems found with these diets were calcium and phosphorus deficiencies (and inadequate calcium to phosphorus ratios), vitamin D excess, and deficiencies in trace minerals (such as iron, manganese, and zinc). One of the home-prepared diets was also positive for E. coli.
Raw food diets that include bones have the additional risk of creating gastrointestinal foreign body obstructions, breaking of teeth, and gut perforations.
The risk of bacterial contamination is a great concern when feeding this type of diets, and also when feeding raw pet treats (such as pig ears). Proponents of these diets claim that dogs are more resistant to gastrointestinal pathogens (such as Salmonella and Campylobacter), but there is no published evidence to support this assertion to the best of this author's knowledge. These pathogens can and do cause acute and chronic gastroenteritis (Sato and Kuwamoto, 1999; Stiver et al., 2003). This is also a significant public health concern, since dogs and cats can shed these microorganisms (Joffe and Schlesinger, 2002; Finley et al. 2007) and contaminate the household environment. Zoonosis is of concern, especially if young, elderly, or immunocompromised people are exposed to the raw food diet and to the pet. Many pet therapy programs ban the participation of pets fed these diets due to concerns regarding the potential for exposure of susceptible persons. When dogs and cats eating this type of diets need to be hospitalized for any reason, some hospitals may refuse hospitalizing (or feeding their diet while hospitalized) due to the risk of contamination for other pets and staff. The presence of these pathogens in meat intended for human consumption is well documented, and that is the main reason why specific guidelines for the handling of raw meat in meal preparations for people have been well publicized. A list of published papers regarding bacterial contamination of raw meats and the possibility of transmission of gastrointestinal pathogens from pets to people is provided below.
According to current scientific knowledge, the risks of feeding raw diets outweigh the possible benefits. Clients who feed raw foods to their pets should be advised of this in order for them to make an informed decision. If home prepared raw diets are fed, consider recommending commercial products that have undergone AAFCO feeding trials. If a home prepared diet is still pursued, a consult with a boarded veterinary nutritionist is recommended, although most boarded veterinary nutritionists do not recommend the feeding of raw animal products and do not balance raw diets due to the above concerns. However, many owners may be willing to try a complete and balanced cooked diet. Home prepared (or even commercial) raw food diets can be sent to a laboratory for nutrient analysis as well. Safe handling of the product and the pet's feces should also be discussed, as well as proper cleaning and disinfecting of contaminated areas. Frequent monitoring of the pet is even more important than in the case of home cooked diets.
References
1. The FDA guidance on raw meat foods is available at: http://www.fda.gov/cvm/Guidance/Guide122.pdf
2. AAFCO. Official publication. Oxford, IN: Association of American Feed Control Office; 2008.
3. Andrea Fascetti. VMB 485 notes (2008).
4. Nutrient Requirements of Dogs and Cats. Washington, D.C.: National Academies Press; 2006.
5. Finley R, Ribble C, Aramini J, Vandermeer M, Popa M, Litman M, Reid-Smith R. The risk of salmonellae shedding by dogs fed Salmonella-contaminated commercial raw food diets. Can Vet J. 2007; 48:69-75.
6. Freeman LM, Michel KE. Evaluation of raw food diets for dogs. J Am Vet Med Assoc. 2001;218(5); 705-709.
7. Joffe DJ, Schlesinger DP. Preliminary assessment of the risk of Salmonella infection in dogs fed raw chicken diets. Can Vet J. 2002;43: 441-2.
8. Morris. Idiosyncratic nutrient requirements of cats appear to be diet-induced evolutionary adaptations. Nutr. Res. Rev. 2002; 15: 153-168.
9. Roudebush P, Cowell CS. Results of a hypoallergenic diet survey of veterinarians in North America with a nutritional evaluation of home made diet prescriptions. Vet. Dermatol. 1992; 3: 23-28.
10. Sato Y. Kuwamoto R. A case of canine salmonellosis due to Salmonella infantis. J. Vet. Med. Sci. 1999; 61: 71-72.
11. Stiver SL, Frazier KS, Mauel MJ, Styer EL. Septicemic Salmonellosis in Two Cats Fed a Raw-Meat Diet. J Am Anim Hosp Assoc. 2003;39:538-42.
Other references regarding raw meat contamination (both for human and animal consumption) and zoonoses:
1. Chengappa MM, Staats J, Oberst RD, Gabbert NH, Mc Vey S. Prevalence of Salmonella in raw meat used in diets of racing greyhounds. J Vet Diagn Invest. 1993;5(3):372-7
2. Clark C, Cunningham J, Ahmed R, Woodward D, Fonseca K, Isaccs S, Ellis A, Anand C, Ziebell K, Muckle A, Socket P, Rodgers F. Characterization of Salmonella Associated with Pig Ear Dog Treats in Canada. J Clin Microbiol. 2001;39(11):3962-8
3. Doyle MP, Schoeni JL. Isolation of Escherichia coli O157:H7 from retail fresh meats and poultry. Appl Envron Microbiol. 1987; 53 (10): 2394-6.
4. Entis P, Lerner I. Twenty-four hour direct presumptive enumeration of Listeria monocytogenes in food and environmental samples using the ISO-GRID method with LM-137 agar. J Food Prot 2000;63:354-363.
5. Finley R, Reid-Smith R, Weese JS. Human health implications of Salmonella-contaminated natural pet treats and raw pet food. Clin Infect Dis. 2006;42(5):686-91.
6. Fredriksson-Ahomaa M, Korte T, Korkeala H. Transmission of Yersinia enterocolitica 4/O:3 to pets via contaminated pork. Lett Appl Microbiol 2001;32:375-8
7. Freeman LM, Michel KE. Evaluation of raw food diets for dogs. J Am Vet Med Assoc. 2001;218(5); 705-709.
8. Jenkins DJ, McKinlay A, Duolong HE, Bradshaw H, Craig PS. Detection of Echinococcus granulosus coproantigens in faeces from naturally infected rural domestic dogs in south eastern Australia. Aust Vet J. 2006;84(1-2):12-6.
9. LeJeune JT. Public health concerns associated with feeding raw meat diets to dogs. J Am Vet Med Assoc. 2001;219(9): 1222-5.
10. Mead PS, Slutsker L, Dietz V, McCaig FL, Bresee JS, Shapiro C, Griffen PM, Tauxe RV. Food-Related Illness and Death in the United States. Emerg Infect Dis. 1999;5(5):607-25.
11. Morley PS, Strohmeyer RA, Tankson JD, Hyatt DR, Dargatz DA, Fedorka-Cray PJ. Evaluation of the association between feeding raw meat and Salmonella enterica infections at a Greyhound breeding facility. J Amer Vet Med Assoc 2006 May 15;228(10):1524-32.
12. Murray SM, Patil AR, Fahey GC Jr, Merchen NR, Hughes DM. Raw and rendered animal by-products as ingredients in dog diets. J Nutr. 1998;128(12 Suppl):2812S-15S.
13. Nash JQ, Chissel S, Jones J, Warburton F, Verlander NQ. Risk factors for toxoplasmosis in pregnant women in Kent, United Kingdom. Epidemiol Infect. 2005;133(3):475-83.
14. Reichel MP. Neospora caninum infections in Australia and New Zealand. Aust Vet J. 2000;78(4):258-61.
15. Samadpour M, Ongerth JE, Liston J, Tran N, Nguyen D, Whittam TS, Wilson RA, Tarr PI. Occurrence of Shiga-Like Toxin-Producing Escherichia coli in Retail Fresh Seafood, Beef, Lamb, Pork, and Poultry from Grocery Stores in Seattle, Washington. App Environ Microbiol. 1994;60(3):1038-40.
16. Sato Y, Mori T, Koyama T, Nagase H. Salmonella virchow Infection in an Infant Transmitted by Household Dogs. J Vet Med Sci. 2000;62:767-9.
17. Schotte U, Borchers D, Wulff C, Geue L. Salmonella montevideo outbreak in military kennel dogs caused by contaminated commercial feed, which was only recognized through monitoring. Vet. Microbiol. 2007; 119: 316-323.
18. Smielewska-Los E, Rypula K, Pacon J. The influence of feeding and maintenance system on occurrence of Toxoplasma gondii infections in dogs. Pol J Vet Sci. 2002;5(4):231-5.
19. Stone GG, Chengappa MM, Oberst RD, Gabbert NH, Mc Vey S, Hennessy KJ, Muenzenberger M, Staats J. Application of polymerase chain reaction for the correlation of salmonella serovars recovered from greyhound feces with their diet. J Vet Diagn Invest. 1993;5(3):378-85.
20. Strohmeyer RA, Morley PS, Hyatt DR, Dargatz DA, Scorza AV, Lappin MR. Evaluation of bacterial and protozoal contamination of commercially available raw meat diets for dogs. J Am Vet Med Assoc. 2006;228(4):537-42.
21. Urban JE, Bruce A. Flies and their bacterial loads in greyhound dog kennels in Kansas. Curr Microbiol 1998;36:164-70.
22. Weese JS, Rousseau J, Arroyo L. Bacteriological evaluation of commercial canine and feline raw diets. Can Vet J. 2005;46(6):513-6.
23. White DG, Zhao S, Sudler R, Ayers S, Friedman S, Chen S, McDermott PF, McDermott S, Wagner DD, Meng J. The Isolation of Antibiotic-Resistant Salmonella from Retail Ground Meats. New Eng J Med. 2001;345(16):1147-54.
24. Zhao C, Beilei GE, De Villena J, Sudler R, Yeh E, Zhao S, White DG, Wagner D, Meng J. Prevalence of Campylobacter spp., Escherichia coli, and Salmonella serovars in retail chicken, turkey, pork, and beef from the Greater Washington, D.C., area. Appl Environ Microbiol. 2001; 67(12):5431-6.