There are many arguments surrounding the correct way to feed a balanced healthy diet to dogs and cats. This article will present the current scientific knowledge from peer-reviewed mainstream journals and peer-reviewed research groups, not views and opinions but proven scientific facts.

It is important when viewing literature that we can identify the type (level) of evidence being written up. Table 1 shows the types of evidence and the levels they represent, Level 1 evidence being of the highest value.

Food contamination

Contamination of all foods is possible, whether raw, home-cooked or manufactured/processed diets. Joffe & Schlesinger (2002) found that 80% of biologically appropriate raw food (BARF) diets contained Salmonella, and, of those pets fed these diets, 30% shed Salmonella in their stools. The Food and Drug Administration (FDA) in the USA estimates that 80% of raw chicken is contaminated with Salmonella. This is chicken sold in supermarkets for human consumption, showing the need for good food preparation and thorough cooking to prevent human infection. This does not, however, remove the potential risk to the animal, if fed raw.

Meta-analyses (Level 1 evidence) have shown that there is a real risk of food contamination from raw meats to both humans and animals (Schlesinger & Joffe 2011). This is an issue that needs to be discussed with pet owners.

Some raw diets that have undergone high-pressure pasteurisation at 100-800 MPa with a slight temperature increase (3 °C/100 MPa) are available, but there is no standardisation of this method of food preparation for these types of diet. Differences will occur with batch size, ingredients used and volume cooked at each time. It should also be remembered that preservatives in pet foods are not included solely to stop bacteria and fungi multiplying, but also to preserve the food ingredients. It is the cooking and extrusion process that removes the bacterial contamination.

Canned diets can be considered sterile, providing there is no damage to the tin. It is important to ensure that raw diets that are supplied frozen are kept at -20 °C, and most domestic freezers are set at a temperature of -18 °C. Of the bacteria, Campylobacter species are the only ones destroyed by freezing; in fact, some bacteria thrive on being frozen! However, this process is good for the control of parasites; Toxoplasma, for example, is destroyed by freezing at -20 °C for 48 hours.

Gastric pH

One factor that is commonly cited in the debate over feeding of processed versus raw/home-cooked diets is the pH differences that these diets produce when fed, the argument being that only dogs fed raw diets have the ‘physiologically correct’ low pH. However, studies have shown that the gastric pH of fasting dogs can fluctuate from 2.7 to 8.3, with a mean of 6.8 ± 0.2 (SE) (Akimoto et al. 2000), and Sagawa, Liese & Sutton (2009) demonstrated that dogs fed a dry commercial diet had an average stomach pH of between 1.08 and 1.26 depending on the volume of dry diet fed.

Nutritional risk

On literature review there were no papers found at Levels 1, 2 or 3 that demonstrate any advantages or disadvantages of feeding a non-commercial diet (raw, home-cooked diets). There is a considerable body of Level 4 evidence that demonstrates the nutritional risks of unbalanced diets, including hypervitaminosis A (Polizopoulou et al. 2005), pansteatitis (Niza, Vilela & Ferreira 2003), osteodystrophy (DeLay & Laing 2002) and nutritional hyperparathyroidism (Kawaguchi et al. 1993).

As a regulated profession in a scientific field we need to give clients information based on evidence, not conjecture. All of the evidence regarding the nutritional risks of these diets is currently based on individual cases, where unbalanced diets were being fed. The difficulty is designing and implementing a nutritionally balanced diet for a given animal’s individual needs. Davies (2014) showed that, even when a recipe for a home-cooked ration for dogs with chronic kidney disease was used and made by qualified veterinary nurses, the diets showed large nutritional variations depending on the sourcing of ingredients, cooking differences and interpretation of the recipe. The recommendation from this study was that very detailed recipes that give specific instructions on ingredients and preparation are required.

Stockman et al. (2013) investigated home-cooked diets and concluded that only experts, board-certified animal nutritionists or veterinarians with advanced training in nutrition should be formulating diets for our companion animals (cats and dogs).

Digestive system

In 2013 it was demonstrated that the genetic make-up of domesticated dogs does differ from wolves (Axelsson et al. 2013). Mutations were identified in key genes that provide functional support for an increased starch digestion in dogs relative to wolves. The results indicate that novel adaptations allowed the early ancestors of modern dogs to thrive on a diet rich in starch, relative to the carnivorous diet of wolves; this could have constituted a crucial step in the early domestication of dogs. The argument that dogs should be fed a diet that reflects one that a wild ancestor would have eaten is therefore invalid.

Sturgeon, Jardine & Wesse (2014) presented results of a study investigating the gastrointestinal microbiota in wolves and in domesticated dogs. The results showed that the faecal microbiota of wolves is highly variable, perhaps reflecting the variable and inconsistent diet of wild canids. In contrast, the faecal microbiota of dogs was more consistent, with no difference in population structure between raw and conventionally fed dogs. The study concluded that diet can have an impact on the faecal microbiota of individual dogs and that the faecal microbial population and structure are relatively consistent among the different feeding groups; finally, feeding dogs raw meat does not result in development of a faecal microbiota more akin to that of wolves.


There are multiple levels of evidence which examine the feeding of commercial diets. These include longitudinal controlled randomised studies, and exploration of the benefits of specific ingredients and nutrients. Rigorous research, including the use of randomised data collection and control groups, needs to be conducted on BARF diets in order to produce Level 2 and 3 evidence which can then be disseminated via peer-reviewed mainstream journals. 


Nicola Ackerman BSc(Hons) RVN CertSAN VTS(Nutr) CertVNECC A1 V1 C-SQP MBVNA

To cite this article use either
DOI: 10.1111/vnj.12174 or Veterinary Nursing Journa VOL 29 pp 298-301

AKIMOTO, M., NAGAHATA, N., FURUYA, A., FUKUSHIMA, K., HIGUCHI, S., & SUWA, T (2000). Gastric pH profiles of beagle dogs and their use as an alternative to human testing. European Journal of Pharmaceutics and Biopharmaceutics. 49(2). pp. 99-102.

K. (2013). The genomic signature of dog domestication reveals adaptation to a starch-rich diet. Nature. 495. pp. 360-364.

DAVIES, M. (2014). Variability in content of homemade diets for canine chronic kidney disease. Ve
terinary Record. 174. p. 352.

DELAY J., & LAING, J. (2002). Nutritional osteodystrophy in puppies fed a BARF diet. Animal Health Laboratory Newsletter. 6. p. 23.

JOFFE, D. J., & SCHLESINGER, D. P (2002). Preliminary risk assessment of the risk of Salmonella infection in dogs fed raw chicken diets. Canadian Veterinary Journal. 43(6). pp. 441-442.

KAWAGUCHI, K., BRAGA, I. S. III, TAKAHASHI, A., OCHIAI, K., & ITAKURA, C. (1993). Nutritional secondary hyperparathyroidism occurring in a strain of German shepherd puppies. Japanese Journal of Veterinary Research. 41. pp. 89-96.

NIZA, M. M. R. E., VILELA, C. L., & FERREIRA, L. M. A. (2003). Feline pansteatitis revisited: hazards of unbalanced homemade diets. Journal of Feline Medicine and Surgery. 5. pp. 271-277.

POLIZOPOULOU, Z. S., KAZAKOS, G., PATSIKAS, M. N., & ROUBIES, N. (2005). Hypervitaminosis A in the cat: A case report and review of the literature.
Journal of Feline Medicine and Surgery. 7. pp. 363-368.

SAGAWA, K., LI, F, LIESE, R., & SUTTON, S. C. (2009). Fed and fasted gastric pH and gastric residence time in conscious beagle dogs. Journal of Pharmaceutical Sciences. 98(7). pp. 2494-500.

SCHLESINGER, D. P, & JOFFE, D. J. (2011). Raw food diets in companion animals: A critical review. Canadian Veterinary Journal. 52(1). pp. 50-54.


J. A. (2013). Evaluation of recipes of home-prepared maintenance diets for dogs. Journal of the American Veterinary Medical Association. 242. pp. 1500-1505.

STURGEON, A., JARDINE, C. M., & WESSE, J. S. (2014). Comparison of the fecal microbiota of wild wolves, dogs fed commercial dry diets and dogs fed raw meat diets. ACVIM Forum Proceedings.

Veterinary Nursing Journal • VOL 29 • September 2014 •