I have avoided writing this essay.
The reason is that, contrary to how it may on occasion appear, I generally do not seek out conflict. Considered debate about scientific evidence and civilized discussions? Yep, enjoy those. However, the acrimony and polarization that frequently accompanies internet discussions about how best to feed dogs? Avoid those like the plague.
But, here’s the thing. I write about dogs and science. Over the last year or so, the number of published scientific studies that examine a particular aspect of raw feeding have continued to accumulate on my desk. I read them, sigh, and place them back on the pile.
My aversion to internet fighting was proving to be greater than my need to write science.
On my desk are three new studies, all in refereed, academic journals, and all reporting about the presence of pathogenic bacterial and parasitic contamination in commercially-produced raw dog foods.
Here is what they say:
Study 1: Dutch epidemiologists with the Division of Veterinary Public Health in Utrecht, Netherlands, tested 35 commercial raw, meat-based diets (hereafter, RMBDs) for the presence of bacterial and parasitic pathogens (1). The researchers purposely selected popular brands that were sold by retailers. All of the samples had been stored according to label recommendations prior to analysis. Results: Escherichia coli (E coli) was found in 30 products (86 %). Twenty-eight foods contained an antibiotic-resistant strain of this microbe and eight were contaminated with a strain that causes serious illness in humans. Listeria species were found in 43 % and Salmonella species were found in 20 % of the tested foods. Several products were contaminated with parasites, but this risk was substantially lower than that of bacterial contamination. Conclusions: Because several of the pathogens that were isolated were zoonotic (i.e. are pathogenic to humans) and because the transmission of antibiotic-resistant bacterial strains is an increasingly serious public health issue, the authors conclude that pet owners should be informed of the potential health risks (to humans and to pets) associated with feeding RMBDs.
Study 2: Although conducted in pet cats rather than dogs, this study is important because it examines the effects of feeding a raw diet on changes in fecal bacterial populations and the potential for exposure to antibiotic-resistant microbes (2). The study enrolled 17 pet cats that were fed dry, extruded cat food or a combination of dry food and canned food (the control group), and 19 cats that were fed a frozen or fresh raw diet. Fecal samples were collected weekly and were analyzed for the presence of antibiotic-resistant forms of species within the intestinal bacteria family of Enterobacteriaceae. In addition, 53 cat foods (18 raw products and 35 dry or canned products) were analyzed for the presence of the same bacteria. Results: In the control group (cats that were not fed a raw diet), 3 of 51 samples (5.9 %) were positive for the presence of antibiotic-resistant microbes. In the raw-fed group, 37 of 57 samples (65 %), collected from 17 of the 19 cats, were positive for antibiotic-resistant bacteria. When present, the concentration of these microbes was also found to be significantly higher in cats fed raw diets. Finally, 77.8 % of the raw foods and 0 % (none) of the cooked foods were found to be contaminated with antibiotic-resistant bacteria. Conclusions: This study found a strong association between feeding cats a raw diet and fecal shedding of antibiotic-resistant bacteria. This association suggests a substantial risk of transmission of antibiotic-resistant bacteria to both the animals and to the owners who handle these foods and who may also be exposed to their pet’s fecal matter.
Study 3: In this study, samples of 60 commercially available, frozen RMBDs were tested for microbial contamination (3). Results: Bacteria of the taxonomic family Enterobacteriaceae were found in all 60 samples (100 %). In half of these (52 %), the concentration exceeded the threshold level considered acceptable by EU regulations. Clostrium perfringens was detected in 18 brands (30 %) and concentrations exceeded the maximum allowed in two brands. Salmonella species were found in 4 samples and Camplylobacter species were isolated in three samples. Conclusions: Like other authors, the researchers recommend that pet owners are informed about the pathogen risks associated with raw feeding. They also go a bit further, stating that in view of the antibiotic-resistance problem, dogs who are being treated with antimicrobials should not be fed raw diets; nor should dogs living in homes with infants, elderly people or immunocompromised individuals because these subgroups are more vulnerable to infection.
Review Study (March, 2019): This is the most recently published paper (4). The authors review more than 30 scientific studies, published in academic journals between 2005 and 2019, that measured bacterial pathogens in raw pet foods. In both Europe and the United States, a high proportion of the tested foods had contamination levels that exceeded the minimum acceptable levels for human meat products. The most commonly isolated pathogens were Salmonella and E coli. Most recently, antimicrobial-resistant forms of several different bacterial species have been reported. Conclusions: The authors conclude that there remains little doubt, based upon the published evidence, that the prevalence of potentially serious pathogens is substantially higher in raw pet food than in heat-treated foods and that these levels may pose a significant health risk to both pets and humans.
The (Raw) Deal: As it stands today, the research evidence regarding benefits and risks associated with feeding raw diets tells us this:
- Health benefits? As with any broad category of feeding, the long-term health benefits of feeding raw foods to dogs is difficult to study. To date, most of the purported advantages of feeding raw are based on personal stories and anecdotes and do not have support from controlled feeding trials. The few feeding trials that have examined general health have reported that dogs fed a nutritionally balanced raw diet remain healthy, but have not demonstrated enhanced health benefits above those of dogs fed other foods. This does not mean that there are no benefits; it simply means that we do not know and that the numerous health claims for raw foods are not based on scientific evidence.
- Improved digestibility and nutrient availability? Some owners select a raw food for their dog because they are interested in feeding less highly processed foods. In the dog food realm, both dry, extruded food (kibbles) and canned foods are highly processed and are almost exclusively produced from non-human grade (i.e. “inedible”) ingredients. The way in which these ingredients are handled and cooked during processing causes moderate to severe changes in protein quality and the loss of some nutrients. Therefore, it is not surprising to find that raw diets are usually higher in digestibility than processed foods. However, both digestibility and nutrient availability are dependent upon the quality of the starting ingredients, as demonstrated by a recent study of raw versus processed chicken. There is also evidence, from several researchers, that raw feeding alters intestinal microbe populations. What is not known however, is the impact, if any, of these changes upon digestive capacity or health.
- Safety? The studies reported in this essay provide evidence that commercial raw dog foods are more likely to be contaminated with bacterial pathogens and with specific strains of these pathogens that are resistant to antibiotics. These results show that dogs and people may be at risk of infection and that these foods are a potential vector for the spread of antibiotic-resistant strains of bacteria to other animals and people.
However, the research says what it says. And currently, there are numerous studies, from different, unrelated laboratories, showing us that commercial raw diets are more apt to be contaminated with potentially harmful bacteria.
This is the science.
Deal with it: If you are a raw feeder, then deal with this information in the smart way. Ask producers about their methods for controlling bacterial contamination, about their quality control measures, and about their company’s recall history. Select foods that have been shown to be free of pathogenic bacteria and have not been recalled. When feeding, avoid handling raw products, wash your hands and food preparation surfaces thoroughly, and monitor your dog carefully for signs of illness or gastrointestinal infection.
The science tells you that these are the facts. It is your decision regarding how to deal with them.
- van Bree FPJ, Bokken G, Mineur R, et al. Zoonotic bacteria and parasites found in raw meat-based diets for cats and dogs. Veterinary Record 2017; November: doi: 10.1136/vr.104535.
- Baede VO, Broens EM, Spaninks MR, et al. Raw pet food as a risk factor for shedding of extended-spectrum beta-lactamase-producing Enterobacteriaceiae in household cats. PLoS One 2017; November: doi.org/10.1371/journal.pone.0187239.
- Hellgren J, Hasto LS, Wikstrom C, Fernstrom LL, Hansson I. Occurrence of Salmonella, Campylobacter, Clostridium and Enterobacteriaceae in raw meat-based diets for dogs. Veterinary Record 2019; March: doi:10.1136/vr.105199.
- Davies Rh, Lawes JR, Wales AD. Raw diets for dogs and cats: A review, with particular reference to microbiological hazards. Journal of Small Animal Practice 2019; March:doi.10.1111/jsap.12300.
Interested in learning more about how to critically evaluate and select the best food for your dog? Read Linda Case’s best selling book, “Dog Food Logic: Making Smart Decisions for Your Dog in an Age of Too Many Choices“.