Questions and Answers on Moldy Grain and Mycotoxins

December 24, 2009 at 8:30 am

The following article appeared in the Ohio State University Extension December 22, 2009 CORN Newsletter and was written by Pierce Paul, Katelyn Willyerd and Peter Thomison:

The 2009 corn crop is providing some challenge to grain users due to various levels of mycotoxins that are being found in individual lots of grain. According to some livestock operations and ethanol plants, levels of deoxynivalenol (vomitoxin) and zearalenone in 2009 crop are unprecedented. Grain deliveries have been rejected because of excessively high mycotoxin levels. Some ethanol plants are starting to discount grain at 3 ppm (vomitoxin), with rejection above 7 ppm. Although we’ve experienced localized problems with ear rots in Ohio in past years, the incidence and severity of ear rots and associated mycotoxins this year is more severe and widespread.

Q1. How bad was the mold and mycotoxin problem in 2009?

Abnormally cool and wet weather during and after silking provided optimal conditions for the development of Gibberalla ear rot that resulted in high levels of mycotoxins contamination of harvested grain.

The fungus Gibberella zeae causes ear rot of corn and head scab of wheat. The fungus produces mycotoxins, most notably vomitoxin (deoxynivalenol, DON) as it colonizes. In general, high levels of disease severity and moldy grain indicate high levels of toxin in susceptible varieties/hybrids. Once the crop has dried down (<20% moisture), fungal growth and vomitoxin production are reduced substantially. In harvested grain, vomitoxin is heat stable and water soluble and will survive many processing, baking and distilling procedures.

Q2. What is the impact of these ear rot mycotoxins?

The Gibberella ear rot fungus produces mycotoxins that are harmful to both humans and animals. These include deoxynivalenol (Vomitoxin) and zearalenone and T-2 toxin, all of which may cause health problems. Therefore, suspect grain should be tested for these mycotoxins by chemical analysis before being fed to animals. As a general rule do not feed any grain with 5% or more Gibberella moldy kernels. Hogs and young animals are particularly sensitive to these mycotoxins.

Sampling and testing of grain are necessary to determine that vomitoxin (deoxynivalenol or DON) is below advisory levels in products. The FDA has set the advisory levels to insure the safety of the food and feed supply. For bran, flour, and germ intended for human consumption at 1 ppm. For grain and grain by-products destined for ruminating beef and feedlot cattle older than four months and for chickens with the added recommendation that these ingredients not exceed 50% of the diet of cattle or chicken at 10 ppm. For grains and grain by-products destined for swine, and all others animals with the added recommendation that these ingredients not exceed 20% of the diet for swine and 40% of the diet for other animals set at 5 ppm.

Mycotoxins in corn are concentrated about three fold in dry distillers grains, i.e. during ethanol production, removing the starch from corn (the content of which can average about 60 percent) concentrates levels of these mycotoxins.

If growers were not aware of the moldy corn/mycotoxin problem at harvest more than likely the corn could have gone into the bin in poor conditions. If proper storage conditions were not maintained, the corn will come out of the bin in very bad, perhaps unmarketable, condition surprising the grower and affecting his bottom line significantly.

Q3. Procedures to sample grain lots for Vomitoxin.

Before pulling samples for toxin analysis, grain handlers should first protect themselves from dust and toxin exposure by wearing a mask, goggles and gloves. Careful attention to sampling, extraction and testing protocol should be followed to accurately measure vomitoxin accumulation in grain. Guidelines have been written based on research done with wheat and barley and are available at the United States Department of Agriculture Grain Inspection, Packers and Stockyards website athttp://www.gipsa.usda.gov/GIPSA/documents/GIPSA_Documents/don.pdf.

To collect a representative sample from the bin or truckload of grain, 5-10 subsamples should be randomly collected from multiple locations. Samples taken only from the central or outer portions of the load or from the beginning and end of the grain stream will not provide an accurate estimate of toxin contamination. For end-gate sampling, sample from the entire width and depth of the stream. For probe sampling, use hand or mechanical probes to sample from the entire bin, in an “X”-shaped pattern, for example. The use of suction or air probes is not recommended when sampling grain for mycotoxins. Once subsamples are obtained, bulked, and cleaned, the grain must be ground uniformly, in a clean grinding apparatus, to resemble flour. Finer particle size increases surface area of the grain and allows for more efficient extraction of vomitoxin.

Q4. How and where to test for mycotoxins?

The most common test for vomitoxin is an ELISA test, which is based on the ability of toxin in the grain to bind to specific antibodies coating the specially-designed sample cups provided with the ELISA kit. These kits are very specific for the toxin being tested (vomitoxin in this case) and will not provide estimates of other toxins in the sample. There are separate kits for each toxin. ELISA-based tests are generally qualitative, providing a yes/no answer for the presence of DON, or semi-quantitative, giving an estimate of DON above certain levels or within a given range. However, quantitative estimates can also be obtained using some ELISA-based test. A color-change will be indicative of vomitoxin presence in the sample. To quantify toxin concentration an additional step of assessing color quality through a well reader or spectrophotometer is required. There is a relationship between the intensity of color in the sample cup and vomitoxin, as determined by a standard curve included in the kit. ELISA’s are easy, quick and affordable, but must be performed carefully to ensure quantifiable and accurate results. Due to the test’s specificity, you must use an ELISA kit specifically designed to detect vomitoxin. In addition, the ELISA kit must be approved for the substrate to be tested (corn, DDGs, wheat, etc).

Individuals who to know what the status of grain lots they have in storage maybe can work with grain handlers with the test or if they want to do there own analysis they can obtain ELISA kits . GIPSA has approved several different types of test kits that use either fluorescence or enzyme linked immunosorbent assay (ELISA) technology. The commercial testmethods approved by GIPSA for official testing of barley, malted barley, corn, oats, and wheat for DON are:

Biopharm – RidaScreen Fast SC for registered users only
Charm Science – Rosa Don P/N http://www.charm.com/content/view/81/274/lang,en/
Diachemix -DON FPA http://www.diachemix.com/
Diagnostix – EZ- Quant, EZ- Tox http://www.diagnostix.ca/
Neogen- 5/5, Agriscreen, Veratox http://www.neogen.com/
Romer – Accutox, Fluoroquant http://www.romerlabs.net/
Strategic Diagnostic Inc – Myco, http://ww.sdix.com/
Vicam – Don FQ http://www.vicam.com

A listing of Laboratories who will test for deoxynivalenol or DON, T-2 which are all terms for the group of toxin of concern can be found at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/mycotoxin%20text2.htm

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