By Charles R. Hurburgh and Alison Robertson
The August 10 derecho left portions of Iowa with broken, uprooted, and damaged corn across a significant portion of the state. Paired with drought conditions across the state, especially in west central Iowa, growers should be on the lookout for mycotoxin issues in this years’ crop, especially aflatoxins and fumonisins, as discussed in “Drought and Derecho Increase Mycotoxin Risk in 2020 Iowa Corn Crop-Scouting and Monitoring Fields”. For fields that are intended to be harvested, considerations for harvest, mycotoxin testing, and storage are presented below.
Harvest and storage of moldy or damaged grain
Mycotoxin contamination is an insurable loss, but for both aflatoxin and fumonisin adjustment, the corn must still be in the field. With this in mind, after any necessary communication with your insurance, affected grain that is harvestable should be harvested and dried as soon as possible. Harvest and handling should be gentle; mechanical injury will exacerbate mold issues that started in the field. Drying and cooling the grain quickly is necessary to hinder fungal growth and further mycotoxin production. In the time between harvest and drying, mycotoxins will continue to increase. Avoid using low-temperature or natural air drying as this just serves as an incubator for Aspergillus fungi. Dry the grain to 1-2 percentage points below what you would for sound, healthy kernels. Affected grain should be harvested, handled, and stored separately, if possible. Consider coring bins; be prepared for the core to contain higher levels of mycotoxins than the rest of the bin as mycotoxins tend to be more associated with broken, damaged and lightweight kernels and fines. The same concept would apply for fractions removed from sound grain by mechanical grain cleaners. Move affected grain out quickly as it will not store.
Sampling and testing grain for mycotoxins
Mycotoxin contamination is often unevenly distributed among corn ears in a field and kernels on individual ears. Not only can incidence be quite variable, but the contamination levels can vary widely among individual contaminated kernels. It takes very small amounts to cause negative health effects—on the level of parts-per-million for fumonisins and parts-per-billion for aflatoxins. The low levels that must be detected, combined with the heterogeneous distribution of contamination, make sampling and testing corn for mycotoxins difficult.
Ideally, for a sample to be representative, 10 pounds of shelled corn obtained from a variety of places in the field, truck, or other lot (or decision unit) would be ground, homogenized, and sub-sampled to obtain a final test sample. If only the amount of material needed for the final test is ground, the total error in the test result skyrockets. In essence, this means that test results are highly unreliable if a representative sample, 10 pounds, is not used. With aflatoxins, as few as 70-80 aflatoxin-contaminated kernels in a bushel (56 pounds) can limit grain end-use, so grinding a large enough representative sample is key to obtaining a reliable estimate of the true lot concentration. Samples that are too small normally give low results, with a few giving very high readings. At points of first receipt of grain from growers, buyers may use some form of rapid test, which can give results in about 20 minutes. This may be performed on individual trucks or on composite samples representing multiple deliveries. Samples can also be sent to testing labs for analysis. A listing of some laboratories that perform fee-for-service mycotoxin analyses, including Iowa State’s own Veterinary Diagnostic Lab, can be found here.
Use of grain
At the elevator, high throughput and limited drying and storage capacities will limit testing capabilities and the ability to segregate problematic lots “on the fly”. Adjustment in the field (when possible) may help to reduce the testing burden and unnecessary commingling of potential highly-contaminated lots. Aflatoxin is an adulterant from a human and animal food safety perspective; blending aflatoxin-contaminated grain with lower- or non-contaminated grain with the purpose of lowering the overall aflatoxin level is illegal. In severe aflatoxin years, FDA has granted blending permissions for specified regions, under supervised conditions with documented and approved end-uses. At the time of writing, no portion of the state has been granted such blending permissions.
Early characterization and quantification of mycotoxin issues is key to facilitating a safe end-use strategy for contaminated grain. Mycotoxins are heat-stable and non-volatile; once in grain, they cannot be destroyed through processing or treatment. Therefore, it is important to direct contaminated grains to a tolerant end-user.
There are acceptable uses for corn having aflatoxin concentrations up to 300 ppb. These levels are given by FDA action levels which range from 20 ppb up to 300 ppb (Table 1). End uses that are particularly sensitive to aflatoxin contaminated corn include anything with human food end-use, dairy cattle (a metabolite of aflatoxin transfers into milk), and fuel ethanol producers. Aflatoxins, fumonisins, and other mycotoxins are concentrated three times in dried distiller’s grains with solubles (DDGS) relative to the level in the corn used for ethanol production. The FDA has recommended limits for fumonisin-contaminated corn used as feed ingredients in for various livestock species and poultry, and the inclusion rates of such contaminated grain in complete feeds (Table 2). Their guidance document also contains the guidance levels for fumonisins in human food products.
*immature animals would include, for example, chickens and ducks less than eight weeks of age; turkeys less than 12 weeks of age; goats, sheep, and pigs less than four months of age; cattle and equine less than six months of age.
*dry weight basis
Source : iastate.edu