I have written previously about the potential risks associated with feeding raw food diets. To date, the science that is available reports that:
- The prevalence of potentially serious microbial pathogens is substantially higher in raw pet foods than in heat-treated foods (see The Raw Deal).
- The belief that freezing raw food kills food pathogens or reduces microbial contamination is not supported by the current evidence (see Frozen).
So, what about some of the other forms of raw diets for dogs, for example, freeze-dried products?
What is Freeze-Drying? Freeze-dry processing is a common type of water removal process that is used to preserve commercial raw pet foods. It involves a three-step process in which the formulated food is first frozen and then exposed to a strong vacuum as the temperature is raised slightly. This causes the frozen water in the food to sublimate, which means that it goes straight from ice to vapor, skipping the liquid phase.
Very Low Moisture Products: Of all food processing methods that are currently used for pet foods, freeze-drying results in the lowest level of moisture remaining in the product – only 2 to 5 percent. Similar to other “gentle” processing approaches such as air-drying and dehydration, freeze drying is purported to preserve more of the nutritional content of the food and to result in less loss of essential nutrients and less damage to food protein. (Unfortunately, studies with pet foods that support this supposition are still lacking).
What about Microbial Contamination? There is however, a recent study that compared the presence of microbial contamination in commercially produced freeze-dried dog foods with that of a group of frozen raw products. Although this was a small study, it provides some needed insight regarding the question of whether or not the freeze-drying process helps to protect raw dog foods from microbial contamination.
The Study: A team of researchers with the Department of Veterinary Public Health at Kasetsart University in Thailand sampled 15 different frozen raw foods and two freeze-dried raw foods. Samples were collected by purchasing foods from both physical (brick and mortar) stores and through on-line pet supply services. The types of meats found in the products included chicken, duck, fish, and beef. Measurement of bacterial counts and species identification took place immediately after thawing frozen products and immediate after rehydrating the freeze-dried products (per package instructions).
Results: The researchers reported the following:
- Food Type: Fourteen of the 15 frozen food samples (93 %) had Total Bacterial Counts (TBC) that exceeded acceptable standard limits set for foods and food containers in Thailand. In contrast, both of the freeze-dried products that were tested had counts that were lower than the allowed limits (i.e. were not considered to be contaminated products).
- Bacterial Species: The most common microbial species identified were Salmonella spp (9 foods), Listeria spp (9 foods), Escherichia coli (7 foods), and Staphylococcus aureus (7 foods). These results are consistent with other reports of microbial contamination in raw pet foods.
- Meat Type Mattered: Foods that were chicken-based were significantly more likely to be contaminated with Staphylococcus aureus and Listeria spp. when compared with other meat forms (beef or fish). However, given the small number of samples tested in this study, this may not be a robust finding.
Take Away for Dog Folks:
This small study can be viewed as a bit more evidence to add to the growing body that we have regarding the safety of raw food diets for dogs. The study’s finding that frozen raw foods had high levels of bacterial contamination at limits that exceeded accepted standards should not be surprising at this point. At question is not whether raw food diets are more likely to be contaminated with microbial pathogens (evidence shows that they are, and that freezing foods does not matter), but rather how owners can choose wisely to minimize risk of transmission to both dogs and humans.
Reducing the water content of a food product is a well-accepted approach to preserving foods, and is used in the preparation of both human and pet food products. The very low moisture content of freeze-dried raw foods appears, at least in the two foods studied here, to significantly reduce the survival of food-borne pathogens at the point of feeding. So, if you feed raw (or are considering it), these results may be helpful as you examine the various options that are currently available.
Cited Study: Kananub S, Pinniam N, Phothitheerabut S, Krajanglikit P. Contamination factors associated with surviving bacterial in Thai commercial raw pet foods. Veterinary World 2020; 13:1988-1991.