No, this is not about a Disney Movie.

But it IS about freezing. The freezing of dog food, actually. Raw dog food.

The number of brands and forms of commercial raw dog foods available to owners has increased dramatically in recent years.  A common type of raw diet is in the form of frozen rolls or patties. Following purchase, these foods are stored in the freezer and portions are removed, thawed, and fed on a daily basis.

Reportedly, the intent of keeping raw foods frozen is to minimize or completely eliminate the risk of microbial growth and transmission. It is believed (and often stated by raw food proponents) that freezing these products prevents the growth of microbes that may be present, thereby reducing or completely eliminating risk of transmission of food-borne pathogens to dogs or to the people who feed them.

But, do we know these beliefs to be true? Is there evidence supporting the oft-stated claim that keeping a raw dog food frozen or refrigerated prevents food pathogens from proliferating?

A study published in the Journal of Animal Physiology and Nutrition in early 2020 examined this question.

The Study: The objectives of the study were to evaluate the microbial quality of commercially available raw dog foods sold on-line and shipped in a frozen state to the consumer. A set of 29 raw foods, produced in Italy or Germany, containing a variety of meat ingredients, were obtained from three different on-line companies. All of the foods were delivered in a frozen state (-18 C/0 F) and were immediately placed into a freezer for storage.  Following 24 hours of storage, samples were thawed at refrigerator temperature (2 C/36 F) for ~ 15 hours and were sampled for microbial analysis. (Note: Samples were still at refrigerator temperature when sampled and did not warm to room temperature). Following the initial sampling, foods were stored at either proper refrigerator temperature (2  C/36 F) or at a slightly higher temperature (7 C/45 F) and were resampled at 24, 48 and 72 hours. All samples were analyzed for both qualitative (species) and quantitative (numbers) of food pathogens.

Results: Well, some bugs were found:

• Time Zero: Significant and potentially harmful numbers of pathogenic bacteria were found in a majority of the foods when they were tested immediately after thawing. Of the 29 products, 19 had total bacterial counts at Time 0 that exceeded the maximum level allowed for meats intended for human consumption. In addition, counts for E. coli were unacceptably high in almost all of the foods (26/29).
• Refrigerated Samples: Unsurprisingly, microbial loads increased significantly over the three-day storage period, even when stored properly at refrigerator temperatures. These findings led the researchers to recommend always feeding food portions on the same day that they are thawed – and avoid storing thawed raw foods in the refrigerator, even for short periods of time.
• Temperature Matters: Storing foods at 7 degrees C resulted in much higher bacterial counts and higher levels of contamination with zoonotic microbial species than did storing the foods at the proper refrigerator temperature of 2 degrees C (again, not surprising).
• Freezing Myths: The researchers conclude that the microbial quality of commercial frozen raw dog foods appears to be poor and carries considerable risk of contamination with zoonotic bacteria. Moreover, these bacteria are present at the time of thawing/feeding and proliferate rapidly with storage, even at proper refrigerator temperatures.

Take Away for Dog Folks: This is not good news, either for the dogs being fed these products or for the owners who are handling them. That said, these results should not be tremendously surprising – numerous previous studies have reported high levels of microbial contamination in raw pet foods (see “The Raw Deal“). What is unique to this study is the examination of microbial contamination to frozen foods immediately following thawing and during short-term storage. The researchers stored the thawed foods at both normal refrigerator temperatures and at temperatures that were slightly higher than normal during the 3-day storage period. They used this approach because time/temperature transgressions due to consumer food mishandling are reported to be common contributing factors to outbreaks of foodborne illnesses in humans. Therefore, it is not unreasonable to assume that breaches in food handling practices occur similarly when dog owners feed raw foods to their dogs. Considering the high initial microbial loads found in many of the foods in this study, coupled with the very rapid increase in microbial numbers during both proper and improper storage, it is obvious that owners should take particular care when handling, storing and feeding frozen raw diets to their dogs. 

Soap Box Time: What this study also tells us is that the common belief that keeping raw dog foods frozen prevents microbial contamination is not supported by evidence. The results of this study showed that a large proportion of commercially available raw dog foods arrived containing levels of microbes that exceeded acceptable limits and that these levels were detectable immediately upon thawing. Keeping the food in the refrigerator led to rapid increases in these numbers, even when products were stored properly (and especially rapidly, when they were not).

So. for those who perpetuate the myth about frozen dog foods and safety – Perhaps it is time to “Let it Go“.

Cited Study: Morelli G, Catellani P, Scapin RM, et al. Evaluation of microbial contamination and effects of storage in raw meat-based dog foods purchased on-line. Journal of Animal Physiology and Animal Nutrition 2020; 104:690-697.

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