Petfood at increased aflatoxin risk from US drought
Protect against contamination by establishing an alert system, mycotoxin-specific sampling protocols and rigorous analytical methods
The summer of 2012 will be remembered as one of the driest and hottest summers in history. The ensuing drought was particularly devastating to the corn-growing regions of the US. (See a map, updated weekly, at http://droughtmonitor.unl.edu.) Apart from the loss in yields, the hot and dry conditions also favor the highly complex interaction between corn and the molds Aspergillus flavus and A. parasiticus. These molds produce aflatoxin—one of the most potent and problematic mycotoxins for pets—in the field during harvest and during storage.
Mycotoxins, including aflatoxin, typically arise as a result of an environmental stress that facilitates mold infestation. For the aflatoxin-producing molds, the most significant influence is damage to the seed coat (pericarp) brought on by extreme drought and heat. With this year’s US corn crop experiencing one of the worst droughts on record, early reports seem to be confirming the presence of high levels of aflatoxin in the crop.
Even setting aside this drought, the number of aflatoxin-related recalls and outbreaks has been increasing in recent years. Aflatoxin is a potent liver toxin, and because of its carcinogenic properties, chronic exposure can lead to tumor formation. Clinical signs in dogs and cats include lethargy, anorexia and jaundice.
While outbreaks in dogs are more common, there have been few natural aflatoxin outbreaks in cats reported. This may be due in large part to the limited use of raw materials that could be contaminated with aflatoxin in the manufacturing of cat food compared with dog food (primarily corn grain).
In the field and during harvest, little can be done to minimize aflatoxin contamination. One strategy is the careful monitoring of corn fields for aflatoxin-producing molds (olive green molds). If high mold presence is visible (more than 10% of the corn ears), harvest should happen early with immediate drying (less than 15% moisture) to minimize mold-growing conditions. Once corn is harvested, good storage practices must be implemented to prevent further mold growth and toxin production.
Because of the risks, alert systems should be in place to monitor corn and its sub-products for aflatoxin contamination to prevent their entry into petfood ingredients and products. Perhaps one of the most challenging aspects of mycotoxin contamination is related to the difficulty in accurately assessing the level of contamination in grains. Molds, both in the field and in storage, tend to thrive in pockets or areas where the right combinations of conditions occur that favor their growth.
As a consequence of these growth patterns, distribution of mycotoxins tends to be non-homogeneous in nature, so mycotoxin analysis can be misleading since the analytical procedure is greatly dependent on the sample collected. It is therefore highly recommended that mycotoxin-specific sampling protocols be implemented to significantly reduce the sampling error. In most cases, these protocols merely require an increase in the number of samples taken and frequency of the analysis.
Many different analytical methods exist, with some being more sensitive and accurate than others. Analytical methods range from simple qualitative (yes or no) field test kits to highly sensitive quantitative methods.
Quantitative aflatoxin analysis should be done with approved methods. Currently, enzyme-linked immunosorbent assay (ELISA), fluorometry and lateral flow test methods are the most frequently used for in-house quick quantitative analysis. Although many of these tests have been validated and approved, it is crucial to evaluate if the methods have been validated in the matrix being analyzed.
Chromatographic methods—high performance liquid chromatography (HPLC) or gas chromatography (GC)—are still considered the standard methods and should be utilized for confirmation. A mycotoxin reference lab should be used for chromatographic analysis, test kit result confirmation and analysis of complex matrices. Reference labs should use AOAC-approved methods or validated in-house methods and should have extensive quality control programs that include frequent analysis of:
- Reference materials;
- Daily quality checks;
- Training; and
- Participation in check sample programs.
Mycotoxin analysis is and should continue to be part of quality control programs in the petfood industry. Since mycotoxins tend to be relatively heat and processing resistant, we must assume that petfoods created with mycotoxin-contaminated raw materials will also be contaminated with these toxins.
As the frequency of extreme and inconsistent weather conditions increases, we should become aware of how those events influence mold/plant interactions and lead to mycotoxin contamination. Accordingly, mycotoxin-specific safety measures must be put in place to minimize mycotoxin concentrations in finished petfoods.