Why do people favour raw food?

Raw feeding began to gain traction in 1990s, following publication of 2 books which were based solely on the author’s personal opinions and beliefs, not scientific evidence, a fact overlooked by most readers. The idea of a ‘natural’ diet seems to appeal to pet owners’ psychological desire to care for and improve their pet’s health through a route that they find simple and understandable. Some owners engage with the concept of feeding a diet more akin to the domestic dog’s ancestral relatives the wolf- a raw meat-based diet (RMBD).

The wolf has been used as a model for proponents of RMBD feeding, with focus on its limited capacity to digest carbohydrates that forms a substantial part of modern conventional dog food. However, studies published demonstrate that dogs are now so genetically evolved away from wolves that they are more adapted to digest starch rich foods than the carnivorous diet of ancestral wolves, owing to different patterns of gene expression [1, 2]. Longevity, differing nutritional and energy requirements are other aspects overlooked by RMBD advocates. It is genetically unfounded to model the diet of the domestic dog on their ancestral wild counterparts. Expertise in feeding zoo kept canids emphasizes the benefit of using conventional processed dog food for the majority of the diet.

RMBD producers have made unsubstantiated claims of better skin and coat, smaller stools and more energy in animals fed RMBD. However scientific evidence is to the contrary, indeed not only that raw diets do not fulfill these claims, but moreover are a significant health risk for dogs.

Dangers of raw food diets

Nutritional Balance

There are no published level 1, 2 or 3 studies demonstrating evidence of nutritional benefit in feeding RMBD [3]. Beyond this, dogs are at risk of nutrition related diseases if fed a nutritionally incomplete or improperly balanced diet in the long term [2]. This not only includes vitamin and mineral deficiencies (calcium/ phosphorus imbalances are typical) but also the macronutrients- protein, carbohydrates and fats. RMBD are commonly formulated without the benefit of feeding trials, thus nutritional inadequacy owing to bioavailability is also a real concern [4]. Dogs of differing sizes, breeds and life stages have differing demands in terms of both macro and micronutrients, something that RMBD do not address.

Bacterial pathogens

Many studies have been conducted into the zoonotic bacterial contaminants of RMBD. E.coli 0157:H7, B lactamase producing E.coli, Campylobacter, Salmonella, Brucella, Listeria monocytogenes, Yersinia enterocolitica have all been reported [5, 6].

A 2 year study conducted by FDA found that raw food diets pose a significant risk of both Listeria spp. and Salmonella spp., which cause food borne illnesses [7]. Listeria spp. and Salmonella spp. are two of the leading causes of death in humans related to foodborne illness in the United Sates [8]. The FDA study found 0.2% of dry foods tested (one sample) tested positive for Salmonella spp., compared to 8% of raw foods. No Listeria spp. was identified in dry foods, whereas 16% raw foods were positive for Listeria monocytogenes [7]. 44% of dogs fed Salmonella spp. contaminated RFBD shed salmonellae with no clinical signs for a week following exposure [9]. Therefore, pets fed routinely on a RMBD are a potential continual source of exposure to family members, children, elderly and immunocompromised are at greater risk. The ‘fur baby’ status many dogs enjoy in households- sleeping on beds and ‘kissing’ faces, will increase risk of exposure to family members.

Pregnant women are known to be much more susceptible to Listeria monocytogenes infection; it is a well-established cause of miscarriage, premature labour, fetal death, neonatal meningitis and sepsis [10]. This is a huge concern. The CDC, NHS UK and other authorities strongly advise avoiding unpasteurized milk and cheeses whilst pregnant. Feeding household dogs RMBD should also be avoided.

Antimicrobial resistance

Heat treatment is a critical step in control and elimination of bacteria, which is not available to producers of raw food. Bacterial species from livestock, both pathogenic and commensal, can carry microbial resistance genes on plasmids. These are small, circular, double-stranded DNA molecules that are distinct from the bacteria’s chromosomal DNA. Bacteria can readily transfer plasmids (and thus resistance genes) to one another through a process called conjugation [11].

Studies found that 28 of 35 raw pet food products yielded Extended Spectrum Beta Lactamase (ESBL) positive E.coli [12, 13]. This gene is typically borne on transmissible plasmids. 23% of poultry based raw food samples yielded plasmid borne AmpC genes [14, 15]. AmpC is another beta lactamase conferring resistance to penicillins and second and third generation cephalosporins and cephamycins. Raw feeding has also been identified as a strong risk factor for shedding resistant Salmonella spp. [3, 16, 17].

Non-bacterial pathogens and zoonoses

Aside from bacterial zoonoses, several non-bacterial pathogens have also been proposed as potential risks for pets fed RMBD and their owners. Neospora caninum, Sarcocystis spp, Toxoplasma gondii, Isospora, Cryptosporidium parvum, Giardia, Echinococcus granulosus, Echinococcus multilocularis, Taenia hydatigena, Taenia ovis and Trichinella have all been detected The risk to humans from T.gondii infected cats is well known; in addition direct infection from the RMBD has also been established [18]. The viability of other pathogens in RMBD is not yet fully characterized.

Foreign body ingestion

Another consideration is the possibility of tooth fracture, intestinal obstruction or perforation following ingestion of bone fragments which these diets inevitably contain. This can result in emergency surgery or even death.

Regulation of production and labelling

American Veterinary Medical Association (AVMA) asserted in 2012 that “Raw pet foods are produced with little or no regulatory oversight by government”. Whilst this may have improved somewhat, derogations exist for small businesses allowing for self-declaration of hazard analysis and preventative controls. This provides a regulatory loop hole for many RMBD producers.

As regards labelling, pet foods are required to have an American Association of Feed Control Officials (AAFCO) nutritional adequacy statement and a guaranteed analysis table; however, more than 25% RMBD brands do not meet these stipulations [4]. There are also no food borne illness warnings included on RBMD labels, despite the risk posed. The USDA requires warning statements placed on raw meat intended for human consumption, similar would be advisable for RMBD for animals.

Conclusion

RMBD are potentially dangerous for dogs owing to nutritional imbalance, foreign body ingestion and exposure to pathogens, including L. monocytogenes and Salmonella. L. monocytogenes infection in pregnant women has very serious health consequences, including miscarriage. RMBD is implicated in spreading antibacterial resistance genes.

The FDA has released a warning about the public health dangers of feeding RMBD. In addition, the American Animal Hospital Association (AAHA) and AVMA officially recommend against feeding raw food diets.

Owners who decide to feed these products in the face of professional advice to the contrary, should take very strict food hygiene precautions, including disinfecting surfaces and vessels and thorough hand washing. They should also be aware that their pet is likely to be a source of potential infection for their family (faeces and mouth), which may alter the interaction, relationship and how they engage with their pet.

Royal Canin advise feeding a commercial diet based on scientific nutritional evidence and feed trials, specifically formulated for the dog type and lifestage, and transparently labelled in accordance with all governing regulations.

References

1. Axelsson, E., et al., The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature, 2013. 495(7441): p. 360-4.
2. Freeman, L.M., et al., Current knowledge about the risks and benefits of raw meat-based diets for dogs and cats. J Am Vet Med Assoc, 2013. 243(11): p. 1549-58.
3. Schlesinger, D.P. and D.J. Joffe, Raw food diets in companion animals: a critical review. Can Vet J, 2011. 52(1): p. 50-4.
4. Mehlenbacher, S., et al., Availability, brands, labelling and Salmonella contamination of raw pet food in the Minneapolis/St. Paul area. Zoonoses Public Health, 2012. 59(7): p. 513-20.
5. Bojanić, K., et al., Isolation of Campylobacter spp. from Client-Owned Dogs and Cats, and Retail Raw Meat Pet Food in the Manawatu, New Zealand. Zoonoses Public Health, 2017. 64(6): p. 438-449.
6. Davies, R.H., J.R. Lawes, and A.D. Wales, Raw diets for dogs and cats: a review, with particular reference to microbiological hazards. J Small Anim Pract, 2019. 60(6): p. 329-339.
7. Nemser, S.M., et al., Investigation of Listeria, Salmonella, and toxigenic Escherichia coli in various pet foods. Foodborne Pathog Dis, 2014. 11(9): p. 706-9.
8. Scallan, E., et al., Foodborne illness acquired in the United States–unspecified agents. Emerg Infect Dis, 2011. 17(1): p. 16-22.
9. Finley, R., et al., The risk of salmonellae shedding by dogs fed Salmonella-contaminated commercial raw food diets. Can Vet J, 2007. 48(1): p. 69-75.
10. Craig, A.M., et al., Listeriosis in Pregnancy: A Review. Obstet Gynecol Surv, 2019. 74(6): p. 362-368.
11. Bennett, P.M., Plasmid encoded antibiotic resistance: acquisition and transfer of antibiotic resistance genes in bacteria. Br J Pharmacol, 2008. 153 Suppl 1(Suppl 1): p. S347-57.
12. van Bree, F.P.J., et al., Zoonotic bacteria and parasites found in raw meat-based diets for cats and dogs. Vet Rec, 2018. 182(2): p. 50.
13. Baede, V.O., et al., Raw pet food as a risk factor for shedding of extended-spectrum beta-lactamase-producing Enterobacteriaceae in household cats. PLoS One, 2017. 12(11): p. e0187239.
14. Nilsson, O., Hygiene quality and presence of ESBL-producing Escherichia coli in raw food diets for dogs. Infect Ecol Epidemiol, 2015. 5: p. 28758.
15. Schmidt, V.M., et al., Antimicrobial resistance risk factors and characterisation of faecal E. coli isolated from healthy Labrador retrievers in the United Kingdom. Prev Vet Med, 2015. 119(1-2): p. 31-40.
16. Leonard, E.K., et al., Risk factors for carriage of antimicrobial-resistant Salmonella spp and Escherichia coli in pet dogs from volunteer households in Ontario, Canada, in 2005 and 2006. Am J Vet Res, 2015. 76(11): p. 959-68.
17. Morley, P.S., et al., Evaluation of the association between feeding raw meat and Salmonella enterica infections at a Greyhound breeding facility. J Am Vet Med Assoc, 2006. 228(10): p. 1524-32.
18. Macpherson, C.N., Human behaviour and the epidemiology of parasitic zoonoses. Int J Parasitol, 2005. 35(11-12): p. 1319-31.

Postdate: 14th Sep 2020