New Mycotoxin Study of Grain-free and Grain-included Dog Foods

Adding to the controversy of grain or no grain, a new study found multiple mycotoxins in grain-included dog foods, and no mycotoxins in grain-free dog foods.

A new study – “Comparison of mycotoxin concentrations in grain versus grain-free dry and wet commercial dog foods” – tested 60 dog food samples; dry and wet foods – grain-included and grain-free. The results of their testing: “Results of the study demonstrated measurable mycotoxin concentrations in dry dog foods containing grains but not in grain-free dry dog foods, or in wet foods either containing grains or grain-free. This study suggests that the risk of mycotoxin exposure is higher in dry dog foods containing grains.”

Excerpts from the study:

Sales of grain-free pet foods increased by 28% in US pet stores during a one-year period from September 2012 to September 2013. In 2015, 45% of all new pet food items introduced were grain-free. One of these perceived health benefits of grain-free diets is the possibility to reduce grain consumption by companion animals, theoretically reducing the risk of potential exposure to mycotoxins. Mycotoxins are secondary metabolites produced by filamentous fungi that can contaminate grains, often due to improper grain storage. The most common contaminants of feed include aflatoxins, fumonisins, ochratoxin A, zearalenone, and the trichothecenes deoxynivalenol, T-2 toxin, and HT-2 toxin. These mycotoxins have a variety of harmful cytotoxic mechanisms.

The clinical effects of mycotoxins vary based on type, concentration, and frequency of exposure. Some mycotoxins cause morbidity and mortality both acutely due to high dose exposures and chronically after prolonged low-dose exposures. Effects can include acute toxicosis such as acute hepatic injury presenting as anorexia, depression, gastrointestinal hemorrhage, jaundice or seizures. Chronic diseases such as liver and kidney fibrosis, infections resulting from immunosuppression, and cancer have been associated with low-dose, chronic mycotoxin exposure. In one clinical study, a combination of mycotoxins including aflatoxin B1, aflatoxin B2, fumonisin B1, fumonisin B2, ochratoxin A, and zearalenone induced immunotoxicity on canine peripheral blood mononuclear cells. Therefore, the potential for mycotoxin contamination in pet food poses a serious health threat.

Regulations regarding permissible concentrations of mycotoxins in animal feeds focus mainly on farm animals used for food production. While much of what is known about mycotoxins in animals is based on toxicological data demonstrating adverse effects in farm and laboratory animals exposed to naturally occurring concentrations of mycotoxins, there is perhaps even more concern for companion animals who are often maintained and fed for longer periods of time on a homogeneous, grain-containing diet and thus more likely to have chronic exposures to pet foods contaminated with either single mycotoxins, or multiple mycotoxins in various combinations. Maximum concentrations permitted in pet foods are generally extrapolated from a generalized “other animal” category, meaning non-food animal guidelines rather than pet-specific regulations. However, these concentrations do not necessarily indicate “safe levels” for mycotoxin exposure in companion animals since very few studies have been conducted in pets. Moreover, none of these studies have investigated the long-term chronic exposures that likely occur if pets are fed a contaminated feed over a typical lifespan. Due to this uncertainty, one of the perceived health benefits of grain-free diets might be due to the elimination of low-dose chronic exposures to mycotoxins, as grains in pet food are presumed to be the main source of mycotoxin contamination.

Unfortunately we don’t have brand names, or any clues to what brands were tested. We are provided information that two brands contained multiple mycotoxins – which increases the risk to the pet.

A total of 60 dog food samples were analyzed for 11 different mycotoxins. Only dry dog foods containing grains had detectable mycotoxin contamination. When considered by brand, at least one of the four Fusarium mycotoxins was found in each of the four brands of dry grain foods. For two brands (Brand 4 and Brand 5), at least one of the three samples tested were positive for all four Fusarium mycotoxins.

In this study, we identify low-level Fusarium-derived mycotoxin contamination in grain-containing dry dog food but did not detect any mycotoxin contamination in either grain-free dry dog food or wet dog food. In addition, none of the analyzed samples contained aflatoxins in detectable concentrations, which may reflect how regulatory and control strategies have been effective in reducing the incidence of aflatoxins in dry commercial dog foods. The presence of Fusarium mycotoxins highlights the need to establish similar control strategies targeting these mycotoxins, especially for the manufacture of dry dog foods. We found Fusarium-derived mycotoxin concentrations well below amounts considered to be acutely toxic to dogs, but these data support the possibility that feeding grain-containing pet food may result in chronic exposure to a variety of mycotoxins. The effects of chronic low-level mycotoxin exposure in dogs remain unknown but merit further study.

Of 12 grain-included dry pet foods tested, 9 tested positive for Deoxynivalenol (75%), 9 tested positive for Fumonisin B1 (75%), 8 tested positive for Fumonisin B2 (67%), and 4 tested positive for Zearalenone (33%). As stated above, of 12 grain-free dry pet foods tested – none were found to contain mycotoxins.

Justifiably so, the study includes a statement regarding the often questionable quality of feed grade ingredients.

When grains are incorporated into dog food formulations it is important that high quality grain is used. Grain quality is correlated with mycotoxin contamination as lower grade grains often contain broken and fragmented grains which are much more susceptible to mold growth and subsequent mycotoxin production. Grains are numerically graded based on factors such as test weight, proportion of damaged or broken kernels, presence of foreign odors, or heat-damage. Any of these factors can contribute to mold growth and mycotoxin production. However, pet food manufacturers may choose grains unfit for human consumption as a cost-cutting strategy. Using only grains graded as US No.1 by the USDA could be a control strategy to minimize mycotoxin contamination from ingredients incorporated into pet food. Currently, there is no requirement to reveal the grade of grain incorporated into pet food, but noting the grade of grains used on the ingredients list could help consumers choose pet foods with more confidence.

Below is an example of the feed grade grains the study was mentioning. This is actual feed grade corn – stored in a open field in Iowa (provided by a resident of the area). This feed grade corn is subject to weather elements (which could increase the risk of mycotoxins) and exposed to wildlife (including animal urine and feces).

Personal opinion: To me, this study highlights a fact of grain-included pet foods that so many scientists, veterinarians, and media of late are neglecting to alert pet owners to – and that fact is the certain risk of mycotoxins common to grain-included pet foods. Even at low levels, over time mycotoxins cause serious health risks to pets. Plus, the risk increases when multiple mycotoxins are present (again, even at low levels). Mycotoxins common to grains used in pet foods ARE a risk and that risk should not be ignored.

To read the full study, Click Here.

To read more about the mycotoxin risks to pets, Click Here.

Wishing you and your pet(s) the best,

Susan Thixton
Pet Food Safety Advocate
Author Buyer Beware, Co-Author Dinner PAWsible
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