July 8, 2021 Raw Re-Visited: Recent Research
Raw diets have previously been discussed on this blog in early 2019, with the ultimate takeaway that the inherent risks associated with raw food diets are not offset by any current evidence of benefit from this feeding method. That position is shared by many public health and veterinary organizations, including the FDA, the CDC, AVMA, AAHA, and WSAVA. However, raw food diets remain an increasingly popular feeding option for pet owners to pursue, both in commercial and homemade forms. The purpose of this update is to review emerging literature from 2020 and 2021, re-evaluating the risk-benefit tradeoff of a raw food diet.
Comparative digestibility between raw food diets and extruded kibble diets has long been an area for further research, complicated by factors impacting digestibility outside of preparation method, such as macronutrient proportions, protein source, carbohydrate sources, and fiber content. These limitations were discussed at length in a 2012 paper comparing macronutrient digestibility between cats fed raw, cooked, and extruded diets. The researchers were able to use identical diets for the raw and cooked groups, with the only difference being the preparation method of the ingredients. This allowed them to directly compare digestibility as impacted by cooking alone-- and they found that cooking a raw meat diet does not alter digestibility. The problem, authors noted, was that the extruded (kibble) diet was not identical to the other two, differing in ingredient composition and adding confounding variables, making it impossible to parse out the role of the extrusion process in altering digestibility, and to what degree. This study provided the ingredients for both the commercial extruded diet and the raw/cooked prepared diets.
March 2021, the International Journal of Veterinary Sciences and Animal Husbandry published a study on the comparative digestibility of raw and dry foods in dogs. This paper involved 10 healthy pit bull dogs, matched for age and weight, fed "dry extruded food [in the] low price range," for the first portion of the experiment and fed "raw food [that ] underwent HPP processing based on chicken meat, using only raw materials suitable for human consumption," for the second portion. The ingredients were not provided for either diet, and the diets varied significantly in their macronutrient composition. The paper ultimately concluded that the raw diet had greater digestibility than the extruded diet, however, discussion on confounding factors was limited. The reported coefficient of digestibility for the dry food diet used in this study was 57.11% +/- 9.14%. However, this finding is significantly lower than the digestibility coefficients reported for extruded diets in other literature, which routinely reaches 80-90%.
The other question that remains is to what degree diet digestibility is clinically significant, so long as the ultimate quantity of nutrients absorbed is sufficient for providing complete and balanced nutrition to an animal. Even if raw diets are more digestible than extruded diets, the health benefits, if any, are unclear. This remains an area for future research, hopefully with the use of identical raw, cooked, and extruded diets, allowing true comparison of digestibility between processing methods.
Proponents of raw food diets often cite improved health outcomes in their dog as a reason for feeding such a diet. To date, evidence of clinically significant health improvements as a result of raw feeding has not been documented, but studies seeking to identify such benefits are increasingly performed. Four such studies are available from 2020 and 2021 to consider.
Published October 2020, a study in Frontiers in Veterinary Medicine assessed the relationship between atopic dermatitis, diet, and gene transcription. This study found that altered gene transcription is seen in dogs affected by atopic dermatitis and that diet can impact gene transcription profiles. This study was limited by the sample size (8 dogs, 4 healthy and 4 with atopy, 2 each for the diet groups) as well as uncontrolled variance in the diets beyond the processing method. In particular, the diets were substantially different in macronutrient concentrations, with the raw diet also being much higher in fat than the extruded diet. The authors additionally propose that the inherent microbial contamination of a raw food diet may enhance passive innate immunity. If this were to be the case, further research would be indicated to evaluate the cost-benefit to pathogen exposure as a means of preventing or reducing atopic dermatitis.
More broadly, three recent studies have assessed the effect of raw diet on measurable blood parameters. In April 2020, researchers published a pilot study in which 33 client owned Staffordshire Bull Terriers, healthy and with atopic dermatitis, were assigned diet groups and had baseline and final blood samples analyzed. While statistically significant differences were noted following the diet interventions, most remained within established reference intervals. No conclusions regarding health impacts on the dogs in this study could be made, and to what degree changes could be attributed to diet processing type as opposed to nutrients was also unclear.
In March 2021, a study was published that utilized 20 pitbull type dogs and fed only a raw food diet, having previously been on a "low-class industrially processed dry extruded food." Over the study period eating raw diets, blood work showed an increase in total protein, urea, and albumin, a decrease in cholesterol, and a decrease in alkaline phosphatase. The clinical significance of these changes were unclear, and there was no comparable group fed a similarly formulated extruded diet.
Finally, in June 2021, the Journal of Animal Science published research that attempted to assess the clinical health differences between dogs fed raw and extruded kibble diets. While the concept of this study would be incredibly useful for characterizing potential risks and benefits associated with real-world feeding of raw diets, this study unfortunately fell short from providing meaningful data on clinical differences between the two groups. The study recruited client-owned, healthy adult dogs that had eaten an extruded kibble or raw food diet for at least one year (>2 years for all but one of the final study group). In the final group of dogs, the dogs eating raw diets were older and had lower body condition scores than the dogs eating kibble diets. Therefore, breed, gender, age, and body condition score were considered confounding factors in regression analysis of the final data. Extensive information on the dog's history was collected. Physical examination of the dogs was blinded, and a "Clinical Health Score" (CCS) was given out of 9 based on a score of 0-3 in each category of oral health, ear health, and skin health, where a score of 9/9 was clinically normal in all aspects of all three categories. When evaluating the significance in score differences, authors used statistical models to control for potentially confounding variables noted in the history, such as frequency of bathing or oral chews. Additionally, all dogs had urinalysis, hematology, serum chemistry, and thyroid panels performed. Fecal consistency was evaluated for all dogs.
As in previous studies, a lower ALP was noted in dogs fed a raw diet, though it was within the reference range for both groups. The clinical significance of this findings remains unknown, but is a valid area for further research, particular in regards to parsing out the role of nutrients vs diet preparation type. In this study, raw fed dogs had a lower total protein, conflicting with previous similar research. Finally, raw fed dogs had a higher lymphocyte count, a category of white blood cells. Given the known risk of microbial exposure in association with raw food diets, this finding could be indicative of infection. However, analysis of the dog's feces was not performed for this study beyond assessment of fecal consistency.
For CCS, there was no difference in scores between the two groups for oral health or ear health. For skin health, scores were significantly improved in raw fed dogs. The authors write that the higher overall CCS in raw fed dogs suggests a "moderate improvement in the overall health." However, based on the provided data, the higher overall CCS appears to be a result only of improved skin health on physical examination, and the role of diet preparation cannot be isolated from the role of nutrient concentration in the diets, such as higher concentrations of omega fatty acids.
The authors of this most recent study write: "Still, it is not possible to conclude that any observed differences between the two feeding groups were due to the diet processing, differences in nutrient composition (protein, fat, or carbohydrate content and quality), or added supplements. Regardless, the current data do support the differences in physiological and general health markers between dogs based on diet." This is ultimately the crux of much of the research currently performed to assess raw food diets in dogs. In order to truly assess the impact of a raw diet, as opposed to a cooked or extruded diet, the diets must be otherwise comparable in all or most other regards, including ingredients, macronutrients, and micronutrients. The information gained from a true comparison of that nature could help shed light on whether the public health risks associated with the use of raw diets is justifiable.
Opponents of raw food frequently cite the microbial risks, present for both animals and their owners, associated with such preparation methods. While such risks are well-documented indirectly, through comparative fecal analysis and other means as detailed in the previous post on this blog, many raw feeding proponents remain skeptical of the actual, real-world significance of these risks. As raw diets become more widespread, it is likely that case reports of illness in association with them will rise. The following six reports detail various recent incidents where these risks have actualized, resulting in illness in companion animals.
Veterinarians in Korea reported in September 2020 two cases of acute polyradiculoneuritis in dogs eating raw poultry diets. Previously known as "coonhound paralysis" due to it's association with recent raccoon contact, this progressive neurological disease causes an ascending paralysis that can ultimately result in death if paralysis affects the diaphragm. For dogs that receive treatment, the prognosis is good, though recovery may take up to 6 months. The authors discuss that a similar syndrome in humans has been linked to Campylobacter infection, and Camplylobacter infection in dogs has been strongly associated with the consumption of raw poultry. In this case, only the second dog was tested for Campylobacter, but was positive for two species. Both dogs ultimately recovered with treatment.
In March 2021, veterinarians at the University of Edinburgh in the UK reported septicemia (bacteria in the bloodstream) and thrombocytopenia (low platelets, a primary cell involved in clotting) in a 5 month old French Bulldog eating a raw food diet. Her blood culture identified Salmonella gallinarum, a serovar of Salmonella unique to poultry. Authors note that this infection also has potential to cause infection in humans, posing a zoonotic risk.
A study published in February of 2020 assessed the feces of dogs for microbes. Dogs were divided into two groups based on consumption of an extruded kibble diet or consumption of some type of raw diet in the previous two weeks before analysis. In the raw fed group, 18 out of 25 dogs (72%) had E. coli, Salmonella, or Campylobacter species in their feces. In the kibble fed group, that number was 5 out of 25 (20%). Isolated E coli strains were multi-drug resistant.
In August 2017, a cluster of genetically similar E coli infections in the UK triggered investigation. A paper published April 2021 detailed investigation of this outbreak. These particular cases involved Shiga toxin-producing E. coli, a particularly dangerous strain. One of the four affected individuals succumbed to their infection. In three of the four cases, investigation ultimately identified raw pet food, specifically tripe, as a plausible source of infection. The authors also note an increase in raw pet food contamination events, potentially attributable to the rising popularity of such diets.
Owner Perceptions & Practices
Finally, considerations about how owners perceive and approach raw diets are important. In May 2021, the Journal of Food Protection published a study on self-reported practices and safety perceptions from owners feeding raw food diets to their pets. This survey collected responses from 174 owners:
95% were confident the raw diet was safe
67% researched food safety information
27% reported rinsing of raw meat (food handling malpractice)
52% don't segregate utensils and surfaces based on exposure to raw meat
89% perceived risk of foodborne illness to be low
While increasingly popular, the proposed health benefits raw food diets remain unsubstantiated and the risks, along with their consequences, continue to show themselves in veterinary clinics across the USA and rest of the world. Those interested in feeding raw food diets for their pet should strongly consider such risks and discuss other options with their veterinarian, including a cooked, fresh diet.
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