Introduction

Raw food or raw meat-based diets are defined as “diets based on uncooked ingredients derived from domesticated or wild-caught food animal species and that are fed to dogs or cats living in home environment”.¹ Ingredients in raw food for pets include skeletal muscle, internal organs, and bones from mammals, fish, poultry as well as unpasteurized milk and uncooked eggs.¹ Raw food feeding has become increasingly popular among pet owners. Especially BARF (originally an abbreviation of Bones and Raw Food but often by supporters translated to Biologically Appropriate Raw Food) feeding has gained increasing interest. BARF is often based on raw meat­based products that are not necessarily nutritionally balanced, but are fed on a rotational schedule, thereby claiming to cover all nutritional needs of the consumer over time.

Marketing are often based on claims that these diets are more natural diets for carnivores and have superior nutritional and health benefits for the animal. Despite these claims being unproven, they often appeal to well-intending pet owners wanting to feed their animal an optimal diet for health and longevity. In the following some of these claims will be discussed based on the currently available evidence:

Pet dogs and cats should be fed what their non­domesticated ancestors or relatives eat because they are metabolically adapted for this diet. Both species are indeed carnivorous and the cat, as an obligate carnivore, depends on animal-derived nutrients. However, the non-domesticated relatives have a very different life compared with our pets. A recent study investigating differences in the genome of dogs and wolves, found that several of the identified dissimilarities related directly to genes involved in starch digestion and fat metabolism. This indicates that pet dogs have changed metabolically to a more omnivore carnivore compared with their wild relatives.² Diets that may be suitable to support the wild relatives with a relatively short lifespan and more intensive reproductive activity may not be optimal for supporting longevity and health in pet animals.

Commercial extruded and canned diets are unhealthy because of the processing as well as inclusion of by-products and chemically synthesized additives and preservatives. Pet food recalls during the past years may have further spurred suspicions for these diets being harmful. During manufacture of pet food, processing such as extrusion of dry food or heating can affect the nutritional quality in different ways depending on degree and time of heating as well as moisture content. Beneficial effects of this processing include increased plant protein and starch digestibility, destruction of anti-nutritional factors, increased amount of soluble fibre, and reduced lipid oxidation. Whereas Maillard reactions, that are heat induced cross-bindings between proteins and sugars and often increase product palatability, may to some extent reduce the nutritional value and protein quality, and heat-labile vitamins (primarily B vitamins and β-carotene) may, to a varying extent, be lost.^3-5 However, because these are known effects of processing, manufactures are able to supplement specific nutrients following extrusion to still secure that the diet is complete and balanced. Inclusion of by-products are generally a globally sustainable and healthy choice compared with using products appropriate for human consumption, they contain natural vitamins and nutrients that complement the diet and decreases the need for additives.

Raw food contains natural enzymes essential for optimal digestion and intestinal function. Enzyme supplementation is generally not necessary to enable dogs and cats to digest their food and enzymes in food will, to a large degree, be denatured in the acidic environment of the stomach. However, a few studies have shown that the digestibility of crude protein in raw diets may be superior to dry food. Whether this difference is due to food related enzymes in the raw food or processing related decreased digestibility of protein in the dry food is not certain, but one study found no differences in nutrient digestibility when the raw meat was cooked before feeding, which could indicate the latter. Furthermore, it is unknown whether this increased digestibility is of clinical relevance.¹

The intestinal microbiota is important for optimal health. In humans, high protein diets have been associated with increased risk of colonic cancer and production of short chain fatty acids (SCFA), such as butyrate seems to have a protective effect. Cats fed extruded chicken­based diets had an intestinal microbiota favouring lactobacillus and bifidobacterium compared with cats fed raw whole chicken, but the clinical consequence of differences in the feline intestinal microbiota is still unknown.⁶

Raw food diets naturally cover the pet’s nutrient needs and are safe.

Comparing nutrient content in 95 bone and raw food rations for adult dogs with recommended allowances, 60% had one or more nutritional imbalances. These imbalances included low calcium and vitamin D content, low iodine, copper, zink, and/or vitamin A content and some included excess calcium.⁷ Further there are published case reports on malnutrition and growth disturbances in puppies fed BARF diets⁸ as well as development of nutritional thyrotoxicosis following consumption of all-meat commercial dog food containing remnants of thyroid tissue⁹.

Raw food feeding significantly increases the risk of the pet harbouring zoonotic infectious agents such as Salmonella sp. and Campylobacter jejuni.^1,10 Often pets are asymptomatic carriers but there are reports on fatal salmonellosis in cats related to infected raw food and there are indications that human clinical salmonellosis and campylobacteriosis are sometimes linked to pets and feeding them contaminated food.

Conclusions

Raw food feeding is primarily marketed through claims that are still unproven. It is possible to feed a balanced diet to the pet based on raw food, but often diets based on homemade receipts are nutritionally unbalanced. Furthermore, feeding raw meat increases the risk of pathogenic bacterial contamination and there is currently no evidence supporting the superiority of feeding the meat raw compared with cooking or frying it before serving.

References

1.  Freeman LM, Chandler ML, Hamper BA, Weeth LP. Current knowledge about the risks and benefits of raw meat-based diets for dogs and cats. J Am Vet Med Assoc. 2013;11:1549–1558.

2.  Axelsson E, Ratnakumar A, Arendt M-L, Maqbool K, Webster MT, Perloski M, Liberg O, Arnemo JM, Hedhammar Ä, Lindblad-Toh K. The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature. 2013;495:360–364.

3.  Singh S, Gamlath S, Wakeling L. Nutritional aspects of food extrusion: a review. Int J Food Sci Technol. 2007;42:916–929.

4.  Hendriks WH, Emmens MM, Trass B, Pluske JR. Heat processing changes the protein quality of canned cat foods as measured by a rat bioassay. J Anim Sci. 1999;77:669–676.

5.  Tran QD, Hendriks WH, van der Poel AFB. Effects of extrusion processing on nutrients in dry pet food. J Sci Food Agri. 2008;88:1487–1493.

6.  Kerr KR, Dowd SE, Swanson KS. Faecal microbiota of domestic cats fed raw whole chicken v. an extruded chicken-based diet. J Nutr Sci. 2014;3:e22.

7.  Dillitzer N, Becker N, Kienzle E. Intake of minerals, trace elements and vitamins in bone and raw food rations in adult dogs. Br J Nutr. 2011;106:S53–S56.

8.  Mack JK, Kienzle E. Inadequate nutrient supply in “BARP” feeding plans for a litter of Bernese Mountain Dog-puppies. A case report. Tierarztl Prax Ausg K Kleintiere Heimtiere. 2016;44:341–347.

9.  Broome MR, Peterson ME, Kemppainen RJ, Parker VJ, Richter KP. Exogenous thyrotoxicosis in dogs attributable to consumption of all-meat commercial dog food or treats containing excessive thyroid hormone: 14 cases (2008–2013). J Am Vet Med Assoc. 2015;246:105–111.

10.  Shlesinger DP, Joffe DJ. Raw food diets in companion animals: A critical review. Can Vet J. 2011;52:50–54.