Raw diets – the solution to everything or a worrying trend? 

Professor Rob Foale

BSc BVetMed DSAM DipECVIM-CA FRCVS

VVS Internal Medicine Specialist

Introduction

Over the past thirty years there has been a marked and significant change in owners’ attitude towards feeding raw diets to their cats and dogs, with the number of owners choosing to feed this way steadily increasing (Michel et al, 2008; Hinney 2018).  The list of benefits of feeding raw that are cited by its proponents are many but include better dental hygiene, fewer gastrointestinal symptoms, shinier hair coats with fewer dermatological problems, fewer allergies, reduced hyperactivity in young dogs but more vitality in older dogs, fewer chronic inflammatory conditions and smaller faecal volume with less flatulence.  It has been estimated that approximately 60% of owners in the Netherlands feed their dogs and cats at least partially on a raw diet (Corbee 2013) whilst approximately 25% of the agility dog owners in North America feed their dogs with raw home-prepared or freeze-dried diets (Dinallo et al 2017). 

Anecdotal reports to the medicine service at VVS also suggest that in some parts of the UK, small animal practitioners are reporting that at least 60%, often more, of their clients are moving to feeding raw meat-based diets (RMBD), usually commercially available ones, so this is a trend that appears to be happening across the western world. 

We have probably all encountered clients who are adamant that moving to raw food has solved their dog’s clinical problems and interestingly, when surveyed, not only are advocates of raw feeding frequently passionate on the issue but they have also been shown to be untrusting of veterinary advice, both with regard to dietary advice but also to general medical advice (Morgan et.al., 2017,).  Furthermore, advocates of RMBD feeding see their decision as an act of care, adopting a more natural approach and moreover, of “doing the right thing”. 

When as veterinary surgeons we always strive to do the right thing for our patients but there is growing concern within the profession regarding the feeding of raw foods (Vet Record, 2017), this disparity of opinion is a potential source of conflict between clinician and client and one which as a profession we need to address.

Are dogs really the wolf in our living room?

It is generally accepted that domestic dogs have evolved from wolves and the first fossilised remains of a dog-like canid reported to be found was in Siberia and dated 33,000 years old (Druzhkova et al 2013).  Fossilised remains of what appear to be dogs buried with human remains thought to be 10,000 – 12,000 years old have been found in Israel (Davis and Valla, 1978).  The exact time when dogs started to be domesticated is therefore unclear, but genomic variation indicating domestication are consistent with this starting to happen approximately 10,000 years ago in Southeast Asia or the Middle East (Pang et.al., 2009; Vonholdt et al, 2010), which is consistent with similar evidence to indicate domestication of goats and cattle in a similar time frame. 

The reasons for the domestication of wolves is unclear; one theory is that they were captured for hunting and guarding, which in turn lead to selection of preferable traits.  However, it is more likely that the change in human behaviour to be less nomadic created settlements with waste dumps on which wolves could scavenge for food, a beneficial behavioural change which could have selected for wolves that became more tolerant of, or even preferenced towards, humans (Coppinger and Coppinger, 2010). 

Regardless of the reasons, reduced aggression and altered social cognition were beneficial traits to both humans and wolves (Hare et.al. 2002)and these changes appear to have been accompanied by anatomical changes relating to reduced skull, teeth and brain size. However, dogs, like wolves in the wild, have a much shorter GI tract when compared to that of humans, and wolves and wild dogs generally eat prey and carrion that is high in protein and fat but low in carbohydrates.  RMBD proponents claim that we should therefore mimic this in our feeding of pet dogs and cats at home.  However, aside from the fact that archaeological data suggests that prehistoric canids were omnivores and not pure carnivores, the questions that arise from this are; firstly, are our dogs today really still like wolves?  Secondly, even if they are, did wild canids really have an ideal nutritional status and then thirdly, is there a physiological or evolutionary basis to support the theory that raw feeding is better than commercially available pet foods? 

What is interesting and potentially pertinent to the raw food debate are that there are clear genomic changes that separate dogs from wolves and some of the changes identified relate to digestion; in a paper published in Nature in 2013, Axelsson and colleagues performed whole genome reconstruction from twelve wolves with worldwide distribution and compared these with whole genome sequences from sixty dogs of fourteen diverse breeds, which resulted in their identification of thirty six genomic regions that probably represent targets for selection during dog domestication.   Nineteen of these regions contain genes important in brain function, eight of which belong to nervous system development pathways and potentially underlie behavioural changes central to dog domestication.  A further ten regions showing signals of selection were identified that contained genes with key roles in starch digestion and fat metabolism, therefore providing evidence that the domestication of wild canids was accompanied by genetic change in their digestive function, and in particular by selection within three genes with key roles in starch digestion: AMY2B, MGAM and SGLT1. 

This therefore strongly supports the theory that there were novel adaptations allowing the early ancestors of modern dogs to thrive on a diet rich in starch and fat, relative to the carnivorous diet of wolves and that these constituted a crucial step in the early domestication of dogs.  Furthermore, this work proves that the genetic changes to enable dogs to digest carbohydrates and to move away from a very high protein and fat carnivore diet have been present for at least ten millennia.  Similar changes to the human genome have also been recorded (Perry et al, 2007),so there appears to be a survival advantage through natural selection associated with these changes. 

Taking comparative analysis further, work by Lyu et al (2018) compared the microbiome of domestic dogs and wolves and showed that, although closely related, the modern canine microbiome has significant function and abundance differences compared to gray wolves, almost certainly as adaptations to domestication and a different diet.  It is therefore apparent that the GI tract of a dog is clearly no longer the same as a wolf and although dogs remain closely related to wolves, the argument that we should feed modern domestic dogs in the same way as their wolf cousins is therefore fundamentally flawed as a result of the adaptive genetic changes that have occurred over the last 10,000 or more years.

Do RMBD really lead to improved health?

However, as there are so many clients who passionately believe that feeding RMBD has led to health improvements in their pets, is there any scientific evidence to support this?  A study published in 2017 (Sandri et al) took eight adult Boxers who had been fed on a commercial, complete diet and changed their diet to one that consisted of raw meat (70%) with rice flour, chickpeas flour, oat flakes, dry ground carrots, algae-derived omega-3 fatty acids and mineral-vitamin complex diet.  Their results showed a significant (p< 0.05) improvement in faecal consistency score, all of the dogs displayed a reduced faecal volume and there was a wider genetic diversity and more even distribution of microbiome population in the dogs after they had been fed the RMBD. 

This increased microbiome diversity is also supported in a different study by Kim et al. (2017).  In light of the growing evidence that the intestinal microbiome has significant effects on human health and the small number of studies showing that multi-valent probiotic supplementation is beneficial in dogs with chronic enteropathy (Rossi et al 2014, White et al 2017), it stands to reason that modification of the microbiome in dogs that occurs with RMBD feeding may also bring physiological benefit to the pets concerned.  Schimdt et al (2018) undertook a well-designed study that showed marked differences in the microbiome and metabolome in dogs fed RMBD or commercial cooked food, which again supports the fact that RMBD do alter the intestinal microbiome, but very interestingly, the dysbiosis index in the dogs fed RMBD in this study went up, which would indicate a negative change on the intestinal microbiome with current understanding (Al-Shawaqfeh et al, 2017). 

However, the authors of the study did recommend further work to investigate what, if any, medical benefits these changes may, or do, bring.  Therefore, although a reduction in faecal volume in dogs fed RMBD has been shown to occur along with the changes in the intestinal microbiome, expanding this to conclude that there are genuine holistic health benefits through a well-designed study is not yet possible.

So maybe there is something still to be found? Despite the frequent and vigorous claims that RMBD markedly improve GI health and are linked to reduced signs of GI disease, there has not been a single study published that the author could find that proves this in a quality peer-reviewed manner.  Indeed, Schlesinger & Joffe (2011) concluded that the evidence advanced for the many claimed health benefits of raw feeding amounted to opinions and claims that were, at best, supported by data that was of “low relevance”.  However, despite this, considering the persistent anecdotal reports from owners, as inquisitive veterinary professionals we need to remain open to the possibility that some patients may improve their GI health on RMDB and that the issue here is actually that the appropriate studies we need to establish how and why this might occur have not been performed. 

As good professionals, it is therefore incumbent on us to undertake this research even if there was opposition from the commercial pet diet manufacturers or some colleagues and professional bodies.  However, by the same token, the owners claiming that RMBD has been the solution to their dog’s problems also often do not know whether the same improvement would be seen with feeding a cooked or commercial prescription diet of some form, so there has to be concern regarding any potential conscious or unconscious bias these owners may have, meaning that any such study would need to be prospective, very well designed and large enough to create statistically relevant and accurate results. 

Relating to the gastrointestinal tract, RMBD advocates also frequently claim that feeding raw reduces dental tartar and gingivitis.  However, an RCVS Knowledge on-line review in 2017 (van Veggel and Armstrong) found that, “no published research evidence currently exists regarding the influence of complete raw diets on dental health in dogs. 

During the literature search for the RCVS review some expert opinion papers were found that referred to dental health and raw feeding.  The reference lists of these papers were scrutinised for relevant evidence, however none of the sources retrieved this way were relevant to the research question for this paper”.  However, this position is contradicted by Marx et.al. (2016) who showed that the chewing of both cortical bone and spongy bone did reduce the volume of dental calculus present in the teeth of beagles over a three-week period.  Further support for this was published by Pinto et al (2020), who also showed that bone chewing does help to reduce dental calculus, but it also showed that there was an increased risk of gingival injury with spongy bones. 

However, both of these studies were relatively small in-patient number and very short in their study duration, so the long-term benefits or any potential negative effects were not reported.  It would therefore appear that again, quality prospective studies are required to establish with clarity whether or not the feeding of RMBD does have a consistently positive impact on the oral and dental health of those animal fed in this way.

The rise of RMBD

So why are RMDB becoming so popular?  There have been a number of papers looking at why RMDB use is increasing so much and a summary of why can be given as:

• Claims of nutritional superiority
• Distrust of commercial food
  • And also a distrust of vets who sell food!
• A desire to be in control
• A desire to “feed more naturally”
• Improved palatability and increased interest in feeding
• Changing human-animal bond

(Empert-Galligos et al, 2018, Morelli et al, 2019 and Morgan et al, 2022)

The major concerns for us as veterinary professionals are firstly the fact that most RMBD proponents state they trust their own knowledge (or that of a breeder) on diet more than that of veterinary surgeons and secondly, possibly more worryingly, that they trust the medical diagnoses reached by their vet significantly less than owners who feed commercial cooked foods.  There is therefore a very real risk of the vet-client bond of trust, that is vital to facilitate appropriate care to every patient, is in danger as a result of this conflict between vets and owners over the issue of RMBD. 

So why shouldn’t we encourage and embrace RMBD?  The answer to this can probably be given under two main headings: nutritional content and the potential health risks associated with RMBD.  There is clear, peer-reviewed, evidence that RMBD risk can be nutritionally deficient, especially when home prepared.  Secondly, there is also a growing and significant body of peer-reviewed evidence available to show that dogs and cats on RMDB are at risk to themselves from, and also shed into the environment, parasites and bacteria that are of concern to both animal and human health, worryingly with increasing numbers of multi-drug resistant bacteria being identified.  It is therefore important to look at both of these issues in more detail:

Nutritional completeness

There are now over 75 companies registered in the UK as RMBD producers and RMBD produced commercially appear to generally be reasonably balanced, but it is important to note that this has not been shown for all life stages so nutritional deficiencies could and do still occur in some situations.  Home-produced diets however have no regulation and have been shown to frequently be imbalanced to detrimental effect, with clinical reports of hypervitaminosis A, nutritional osteodystrophy, nutritional secondary hyperparathyroidism and canine hyperthyroidism all occurring in patients fed RMBD (Schlesinger & Joffe, 2011; Hall et al 2020).  These arguments are countered by RMBD proponents by saying that feeding a variety of different food types prevents this (Strauss, 2007), but again, there is a lack of well-designed controlled studies to prove this is the case, so work clearly needs to be undertaken in this area and at the current time concern has to be given regarding the nutritional completeness of home-prepared RMBD, especially in very young patients.

The potential health risks associated with RMBD

However passionate RMBD advocates are with regard to the benefits of feeding a raw diet, there is a growing body of peer-reviewed evidence available to show that dogs and cats fed RMDB are at risk to themselves from, and also shed into the environment, parasites and bacteria that are of concern to both animal and human health, with increasing numbers of multi-drug resistant bacteria being identified, both by being excreted from patients fed RMBD and sometimes present in the food itself (Beade et al, 2017; Bojanic et al, 2016; Davies et al, 2019; Nüesch-Inderbinen 2019; O’Halloran, 2020; Runesvard et al, 2020; van Bree et al, 2018). 

One key to this is that most commercially available RMBD are frozen at -20⁰C, which is alleged to kill all pathogens.  However, although freezing does significantly reduce the parasitic burden, it often does not eliminate it completely and more worryingly, freezing does not reduce the bacterial burden that cooking would usually kill and the thawing process that is required prior to serving the food facilitates rapid bacterial growth to re-start.  It is the risk of pets shedding both parasitic and bacterial infections into the environment and causing illness both in themselves and other pets, let alone humans, that is creating passionate advocates against the feeding of RMBD, with Dr Mike Davies, an RCVS-Recognised Specialist in Nutrition stating in 2017 that “feeding raw meats to pets is reckless, irresponsible and ethically questionable”. 

Furthermore, the US FDA have issued formal public health warnings regarding feeding RMBD and have advised against owners doing this whilst the American Animal Hospital Association, the Canadian Veterinary Medical Association and the World Small Animal Veterinary Association have all concluded that the risks of feeding RMBD outweigh any potential benefits there may be and have recommended that RMBD are not used.  So, what is the evidence to support these positions?  The following is by no means an exhaustive literature review but gives an oversight of the range and quality of the published data supporting these positions:

Salmonella spp. are found in some apparently healthy dog faeces and a review of the literature produces a range of shedding incidence, with more recent papers showing a generally lower incidence than is often considered to be normal:

• 15% in study of 1626 dogs in Florida (Galton et.al. J Infect Dis. 1952)
  • 4.4% in study of 474 dogs in Iran (Shimi et.al., Vet Rec. 1976)
  • 0.0% in study of 150 dogs in New Zealand (Timbs et al., NZ Vet J., 1978)
  • 3.6% in study of 1391 dogs in Trinidad (Seepersadsingh et.al., J Vet Med B Infect Dis Vet Public Health 2004)
  • 2.1% in study of 437 dogs in Taiwan (Tsai et.al., Vet.Res.Commun. 2007)
  • 1.2% in study of 251 dogs in Canada (Proctor et.al., Zoonosis Pub.Health, 2014)
  • 0.23% in study of 436 dogs in UK (Lowden et.al, BMC Vet Res., 2015)

However, when dogs fed RMBD are assessed, the incidence with which salmonella is identified in their faeces is considerably higher; Joffe and Schlesinger (2002) studied 10 test dogs and 10 control dogs and showed the presence of salmonella spp. in 80% of the RMBD samples and that 30% of the dogs being fed these diets were shedding salmonella in their faeces (mainly S. Braenderup, S. Hadar and S. Schwarzengrund).  However, there was 0% contamination or faecal shedding identified in the control dogs fed a commercially available cooked diet.  Morley et al (2006) studied 138 dogs in a breeding facility, all of whom were fed RMBD.  Faecal, food and environmental samples were taken and it was found that 63% of all samples were positive for Salmonella spp. with 93% of faecal samples being positive for Salmonella. 

This study was triggered after three puppies from the facility had been diagnosed with salmonella sepsis on PME at Colorado State University Veterinary Teaching Hospital.  Lefebvre et al (2008) obtained faecal samples from 200 apparently healthy Pets As Therapy dogs every two months for one year, 20% of which were fed RMBD, 80% were fed commercial cooked food.  The incidence of dogs fed RMDB having salmonella identified in faeces was 0.61 cases/dog-year, compared with 0.08 cases/dog-year in dogs that were not fed raw meat (P < 0.001).  Furthermore, the dogs that consumed raw meat were significantly more likely to test positive for salmonella at least once during the year than dogs that did not eat raw meat [odds ratio (OR) 22.7; 95% confidence interval (CI) 3.1–58.8; P < 0.001].  In addition, raw meat consumption was also significantly associated with shedding ESC E. Coli (OR 17.2; 95% CI 9.4–32.3).  This study is particularly concerning as Pets As Therapy dogs are by definition frequently in contact with humans who may be unwell and therefore potentially more susceptible to contracting infection. 

Support for the concern regarding asymptomatic shedding of salmonella spp. can be found in a large multi-laboratory (involving eleven hospital laboratories) collaboration in the USA between 2012 and 2014 and published in the Journal of Clinical Microbiology; this study found that the overall prevalence of Salmonella in cats (3 of 542) was 1% and the prevalence in dogs was 2.5% but diarrhoea was present in only 55% of positive dogs, indicating that active shedding can occur without clinical signs of illness.  The salmonella-positive dogs were significantly more likely to have consumed raw food (P < 0.01), to have consumed probiotics (P < 0.002), or to have been given antibiotics (P < 0.01) and the study identified consumption of raw food as a major risk factor for salmonella infection. 

The link with salmonella to raw food has also come from individual case reports such as the one from Alberquerque et al (2023), which describes a young French bulldog who was treated for salmonella septicaemia and a severe (presumed immune-mediated) thrombocytopaenia caused by S. gallinarium.  Although a sample of the food was not available for analysis, the fact that the dog was a puppy fed exclusively on a poultry-based raw diet, had hardly been outdoors, had not had contact with other dogs and S. gallinarium is host-specific to poultry, it was concluded it was highly likely that the dog had contracted the infection from her raw diet.  Cats are also not immune to the concern, as illustrated by Giacometti et al (2017) in a case report of two cats in the same household fed RMBD that presented for anorexia, V+ and D+.  Salmonella was identified in their food samples and on PCR in one of the cats.  No other infectious agent identified in second cat and presumed Dx of salmonellosis made.  Both cats recovered with treatment.

Another major and potentially significant bacterial pathogen that has been repeatedly associated with the feeding of raw food is E. Coli.  Groat et al (2022) published a study of faecal samples from 190 dogs across the UK, of which 114 fed RMBD and 76 fed cooked commercial food.  Interestingly, in this study only 4% of the RMBD dogs shed salmonella, but no shedding at all was identified in the commercial diet-fed group.  However, antimicrobial-resistant, multi-drug-resistant and third-generation cephalosporin resistant E. Coliwere significantly more likely to be detected in raw fed (54, 25 and 31%, respectively) compared to non-RMBD fed (17, 4 and 4%, respectively) dogs. 

In light of the increasing concern relating to the impact that multi-antibiotic resistant strains of bacteria are having on both human and animal health, this study raises significant concerns regarding the potential and unseen risks that could come with feeding RMBD.  A very sad case report highlights the risks associated with E. Coli further;  Kaindama et al (2021) described the case of four connected people who contracted shiga toxin-producing E.Coli, one of whom subsequently died of haemolytic uraemic syndrome.  Three of the four patients had direct contact with dogs fed RMBD and the causal bacteria was identified in two RMBD samples obtained that the dogs in question had been fed.  It is true to say that there was no conclusive evidence that the patients contracted their infection from the dogs, but there was very strong indication that they contracted it from handling and preparing the raw tripe RMBD.

Further evidence indicating potential harm to human health as a result of the shedding of multi-resistant bacteria comes from a number of studies looking at dogs fed RMBD and then comparing whole genome sequencing analysis of the resistant E. Coli shed by the dogs with either in-contact humans or non-incontact humans in a similar geographical area.  The conclusions these studies reached were that feeding raw food (either home-prepared or commercially available RMBD) was statistically associated with a significantly increased risk of the dogs shedding multi-drug resistant E. Coli and also that there was clear genetic evidence to support transmission of these MDR E. Coli both to the in-contact humans and also through the environment to other non-contact humans, thereby indicating that there a genuine human and one health risk associated with feeding RMBD (Hong et al, 2019;  Kidsley et al, 2020; Mounsey et al, 2022; Toombs-Ruane et al, 2020)

The identification of potentially harmful pathogens in commercially available RMBD products is obviously concerning but there are plenty of reports that do.  Treier et al (2022) published a Swiss study conducted in 2021 that analysed 59 commercially available RMBD’s; 59% of the diets tested positive by PCR for shiga toxin-producing E.Coli and of these, 29% were considered to be of the highly pathogenic sub-type.  In total, 20 different serotypes identified.  The paper concluded that: “Considering the low infectious dose and potential severity of disease manifestations, the high occurrence of shiga toxin-producing E.Coli in RMBDs poses an important health risk for persons handling raw pet food and persons with close contact to pets fed on RMBDs, and is of concern in the field of public health”. 

Further concern comes from a paper from the Netherlands (van Bree et al 2018) which analysed samples of commercially available RMBD and found that E.Coli O157 was identified in 23% of products, ESBL E. Coli found in 80% of products, Listeria monocytogenes was present in 54% and other Listeria species in 43%, Salmonella species in 20% and with regard to parasites, Sarcocystis cruzi was identified in 11%, S. tenella in 11% and Toxoplasma gondii 6%.  Whilst cooked commercial food is certainly not immune from contamination and product recalls, this level of pathogen contamination in commercially available products that claim to be safe is extremely concerning. 

The presence of significantly resistant E. Coli in RMBD samples was corroborated by Baede et al (2017) in a study from Utrecht Veterinary School that assessed faecal samples weekly for three weeks from 17 cats fed cooked commercial food (control) and 19 cats fed commercial RMBD.  ESBL-producing bacteria were isolated from 3 of 51 (5.9%) samples in the control group compared to 37 of 57 (89.5%) samples in the RMBD group and ESBL-producing Enterobacteriaceae were isolated from 14 of 18 (77.8%) raw pet food products and 0 of 35 non-raw pet food products.  The paper therefore concluded that there was a significant association found between ESBL shedding and feeding raw pet food products with a significantly high odds ratio of 31.5.  Further concern regarding the potential risks of antibiotic-resistant bacterial strains in RMBD can be found in a study from Brazil (Ramos et al 2022) which analysed the faeces of 87 dogs fed RMBD and 127 dogs fed a commercially available cooked diet and showed that ESBL-producing E.Coli were only found in dogs fed RMBD. 

Within these patients, high rates of resistance to trimethoprim/sulfamethoxazole (44.3%), ampicillin (34.9%), and ciprofloxacin (34.9%) were detected in the E. Coli identified in the RMBD group, E. Coliisolates from dogs fed RMBDs were more frequently resistant to 9 out of the 11 tested antimicrobials (p < 0.01) and the E. Colifrom dogs fed an RMBD were more frequently multidrug-resistant (p < 0.01).   The fact that there are papers from a number of different countries showing that RMBD is highly significantly associated with faecal shedding of multi-resistant strains of bacteria known to be detrimental to both human and animal health therefore suggests that this is likely to be a repeated problem wherever RMBD are sold and indicates that there is a significant problem with commercial RMBD preparation.

Campylobacter is responsible for many cases of human food poisoning around the world with over 56,000 cases being reported in the UK each year (Food Standards Agency Campylobacter Source Attribution Study 2022).  A 2016 study from New Zealand (Bojanic et al) assessed 50 commercially available RMBD samples along with assessing 110 client-owned cats and 90 dogs for evidence of campylobacter spp.  28% of the RMBD products contained campylobacter spp whilst 36% of the dogs faecal tested positive for campylobacter spp (C. jejuni, C. upsaliensis and C. helveticus; 13%, 23% and 1% respectively).  Dogs fed the RMBD were 12.3 times (95%CI, P = 0.03) more likely to carry C. upsaliensis than those dogs eating dry diets (and interestingly, intact dogs were 4.6 times (95% CI 1.6–14.8, P = 0.002) more likely to carry campylobacter spp.).  There is therefore a significantly increased risk of exposure to campylobacter for the owners of dogs being fed RMBD.

Brucella is a growing concern for all veterinary professionals that appears to be associated with the rise of imports of dogs from Eastern Europe.  However, RMBD may also be a potential source of this dangerous pathogen; Marloes et.al. (2018) describe a case report from the Netherlands of a dog that contracted Brucella suis despite having no history of typical exposure risks but that was fed a raw meat diet using hare carcases imported from Argentina.  Track and trace techniques revealed that the most likely source of infection was the imported raw meat diet.

Bacteria that are much less commonly associated with human food poisoning have also been linked to the consumption of RMBD by domestic pets. O’Halloran et al (2020) described a case series of 47 cats across the UK diagnosed with, or very strongly suspected to have, M.bovis tuberculosis.  All 47 cases were fed a commercially available venison RMBD and four of the owners and one veterinary surgeon who had had contact were found to have latent infection, with one owner requiring treatment.   Although it was not possible to conclusively demonstrate a zoonotic origin for these infections neither was it possible to eliminate the possibility, thereby providing compelling evidence that the commercial raw diet of these cats was the likely route of M. bovis infection in this outbreak of cases.

The potential risks associated with RMBD are not restricted to bacterial infections; Allen et al (2022) describe a case report a 1-year 11-month intact female Alaskan Malamute in the UK fed a raw food diet that was referred for further investigation of hyporexia and increased hepatobiliary enzyme activities.  Clinicopathological and imaging findings were consistent with cholangiohepatitis and coccidial zoites identified on bile cytology.  PCR and amplicon sequencing from the bile identified Hammondia heydorni, a sarcocytid coccidial protozoa with an obligate 2-host life cycle.  The dog was treated with clindamycin, marbofloxacin, ursodeoxycholic acid (UDCA) and S-adenosylmethionine/silybin with complete clinical and biochemical resolution documented after 6 weeks.  Interestingly, Hammondia spp have been previously identified in RMBD samples along with toxoplasma and sarcocystis (Overgaauw 2020).

These papers, which are by no means an exhaustive list of reports, give a clear indication that there is a genuine risk associated with feeding RMBD to the animals receiving it, their owners and the wider population.  As already explained, these papers given also really only scratch the surface, as other conditions for which RMBD have been implicated as possibly being associated with include:

• Yersinia spp
• Brucella spp
• Staphylococcus aureus
• Clostridium spp
• Bacillus cereus
• Bacillus anthracis
• Burkholderia
• Neosporum caninum
• Sarco-cystis species
• Toxoplasma gondii
• Isospora species
• Cryptosporidium parvum
• Giardia
• Echinococcus granulosus and E multi- locularis
• Taenia hydatigena, T. ovis and Trichinella species

Away from the risk of carrying and potentially transmitting infectious disease, a recent paper also makes a potential link between the feeding of home-made cooked and raw diets with an increased statistical risk of dogs developing cancer (Bianco et al, 2020).  Although this study only looked at 345 dogs via a global on-line survey, it is clear that further investigation is required to see if this is a consistent finding or not.

The one question that these papers do not attempt to answer is, aside from highlighting the potential risks, actually how common are human infections caused by RMBD?  This is obviously a crucial question and there is a surprising paucity of information in this regard.  There was a large-scale study based on an internet questionnaire published in 2019 (Anturaniemi et al), which received responses from 16,475 households across the world and concluded that the incidence of human infection related to the feeding of RMBD was 0.2%, which is obviously much lower than indicated by any of the studies quoted previously.  That being said, if approximately 60% of the twelve million dogs now estimated to in live the UK  are fed RMBD as would be the case in The Netherlands, that would still equate to over 14,000 incidents of human infection directly related to the feeding of RMBD per annum.  However, this internet-based study only engaged people who fed RMDB already and as has already established, RMBD proponents strongly believe that their actions are better than feeding commercially cooked food. 

Therefore, whilst it is certainly possible that these data are accurate, there is also a strong possibility that there is an inherent bias in the study towards under-reporting RMBD-induced human infections due to the conscious and subconscious bias that RMBD proponents hold.  Further work therefore clearly needs to be undertaken to establish whether or not the risks that have been clearly shown to exist translate into a similar disease incidence rate or not.

So what conclusions should we draw?

Firstly, whilst this has become a passionate, polarised debate that potentially puts vets in conflict with owners, it is appropriate and accurate firstly to say that the evolutionary debate that feeding RMBD is “more natural” for the GIT of a domestic dog is fundamentally flawed on a genetic basis.  It is fair to say there is some, albeit limited, evidence that RMBD feeding does more to satisfy feeding behaviour instincts, but there is no peer-reviewed published data to prove, let alone consistently, that RMBD are better or lead to improved health for dogs and cats compared to commercially available cooked diets. 

There is some, albeit again very limited and sometimes contradictory, evidence that RMBD creates a more balanced microbiome, but proving what benefit (if any) derives from this has yet to be established and the anecdotal “evidence” of improved oral health, GI health, a better immune response and lower disease incidence simply has not been backed by any well designed, blinded, peer-reviewed or published studies.  This all being said, the debate concerning the carbohydrate-rich diet many humans, cats and dogs in the western world have and the potential negative health implications this may bring also needs further work and we should all remain open to the possibility that there are negative health connotations associated with the modern, carbohydrate-rich diets that many of our patients are being fed and that maybe RMBD do counteract these to some degree. 

As good scientists as well as good clinicians therefore, we need to recognise that not having good evidence could be because good questions have not been asked and good studies have not been carried out.  Consequently, there is a strong argument that it is incumbent on our profession to respond to this challenge and set out to answer these questions by collaborating to design, undertake and report high quality studies such that we have a much better evidence base with which to work and to enable us to know really what, if any, the benefits of RMBD are. 

What we do have at the present time however is clear, repeatable and unambiguous evidence that RMBD feeding poses a significant risk to public and animal health of bacterial and parasitic disease and, if unchecked, could lead to a growing one health issue, especially in light of the growing evidence relating to the shedding of multi-resistant and highly pathogenic bacterial strains and their transmission to humans.  As a consequence, the WSAVA, CVMA and AAHA have all advocated that RMBD cannot be recommended for use in dogs and cats (WSAVA 2020). 

Therefore, on the current available evidence, RMBD cannot claim to be the solution to everything and actually, with regard to the potential infectious disease risk, they do appear to be a very worrying trend.  As professionals, we need to recognise the desire of our clients to do what they genuinely believe to be in their pet’s best interests and their genuine belief that they are doing this through the feeding of RMBD, but we need to balance this with our obligation to be the advocate for our patients and our duty to do what is in the best interests of every animal entrusted into our care as well as the public in general, which therefore necessitates us working with and educating our owners to feed safely and ethically based on rational, well designed, proven science.  Even if we do eventually prove that RMBD bring consistent health benefits to the dogs and cats that receive them, much work has to be done to ensure that their use is safe for each pet, their owners and the wider public.

If you would like to discuss a clinical case with Professor Rob Foale or any of the VVS Internal Medicine team get in touch by clicking the link below or email the VVS team at [email protected].

References:

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