Corn Rot

Reports from the field suggest that vomitoxin may be higher near tree lines around the perimeter of corn fields. Figure 1. Gibberella ear rot.

High vomitoxin levels are leading to the rejection of some corn at grain elevators this year. Vomitoxin detected in corn so far is enough that at some elevators, trucks are not permitted to leave scales until a vomitoxin quick test is completed. One central Ohio elevator has been rejecting corn at 5 ppm, with estimates of 10% of corn being rejected this season. The average level of vomitoxin in corn passing through central Ohio elevators is estimated at 2 ppm. What exactly does this mean for livestock owners who use this corn as a source of feed?

Vomitoxin, or deoxynivalenol (DON), is a secondary metabolite or mycotoxin produced by Fusarium molds that can cause health and productivity issues in livestock. The common source of DON in corn is the species F. graminearum, which is also occurs in other small grains such as wheat, barley and oats. Some livestock species, such as swine, are more sensitive to DON, while ruminants can typically transform the toxin into a less toxic product as it passes through their digestive tract (due to their rumen microbes). However, age and immune status among other factors can play a role in determining an individual’s sensitivity to the toxin as well.

Fusarium molds that produce DON often develop under wet weather conditions. This particular mold initially enters plants through silks or wounds, and cool, wet conditions during the silking stage promotes spore production, increasing the inoculum load that can potentially infect more plants. Infections by the fungal species F. graminearum result in the development of Gibberella ear and stalk rots (see Figure 1 above) – corn from fields with this disease issue may need to be tested for potential contamination.

Reports from this year’s crop indicate contaminated corn is primarily located along the perimeter of fields – these areas often contain tree lines that tend to reduce dry down after rainfall or produce heavy dews that create optimal conditions for the Fusarium fungus to thrive. Delayed harvests when a significant amount of moisture is present also provides the right conditions for the fungus to further develop and produce the DON mycotoxin.

Symptoms of vomitoxins in livestock include, as its name suggests, acute temporary nausea and vomiting, along with fever and other immunological and productivity issues. Livestock may also refuse contaminated feedstuffs. Feed refusal, ketosis, reduced milk production, diarrhea and displaced abomasum can occur at levels as low as 1.5 – 2.5 ppm of the total ration dry matter for cattle, even though ruminants are less sensitive to vomitoxin compared to non-ruminants such as swine. Of course, we would rather not get to the point of seeing symptoms, so testing of suspected feedstuff can be a key step in identifying a problem. Visual inspections can help identify mold issues but are often not enough for detecting mycotoxins – mycotoxins can be present even if no mold is observed.

The Food and Drug Administration has set the following advisory levels for vomitoxins (on an 88% dry matter basis):

  • For ruminating beef and feedlot cattle >4 months old: 10 ppm on grains and grain by-products; 30 ppm for distillers grains, brewers grains, and gluten feeds / meals derived from grains; total ration should not exceed 10 ppm and 50% of the diet

  • For ruminating dairy cattle >4 months old: 10 ppm on grains and grain by-products; 30 ppm for distillers grains, brewers grains, and gluten feeds / meals derived from grains; total ration not to exceed 5 ppm
  • For chickens: 10 ppm on grains and grain by-products, not to exceed 50% of diet

  • For swine: 5 ppm on grains and grain by-products, not to exceed 20% of diet

  • All other animals: 5 ppm on grains and grain by-products, not to exceed 40% of their diet

Grains exceeding advisory levels can be diluted with uncontaminated corn and other feedstuffs during rationing to reach the diet percentages listed above. Keep in mind that DON also becomes more concentrated in distilled by-products.

Development of the Fusarium fungus, and subsequently DON, will cease when moisture levels fall below 22 percent – a general recommendation is to store feedstuffs at moisture levels below 13% to prevent mold development. Ear corn can be stored at 18 to 20% whole ear moisture only when good air circulation is provided. Although growth and development of the mold stops at this point, DON mycotoxins already produced when moisture levels were greater will still be present in the grain and do not degrade significantly over time.

Care should be given to minimizing conditions that promote condensation in storage such as temperature changes. Removal of lighter, scabby kernels will also allow for better storage of grain. Heat processing and ensiling do not remove mycotoxins, but using silage preservatives or additives can prevent further mold development in storage. High DON levels may warrant the use of a mycotoxin inhibitor – however, these may not be cost effective if DON is present at low levels, and keep in mind that while some inhibitors are effective when applied at the appropriate rates, not all inhibitors are equal in performance.

If you suspect contaminated feed or have symptoms of which the cause cannot be determined, work with your veterinarian and nutritionist and test samples of feed for DON and other potential mycotoxins. For more information on testing for vomitoxin, visit Penn State’s “Mold and Mycotoxin Problems in Livestock Feeding” available at https://extension.psu.edu/mold-and-mycotoxin-problems-in-livestock-feeding and read Pierce Paul’s article “Corn Testing Positive for Vomitoxin: How Reliable was the Sampling?” available at https://agcrops.osu.edu/newsletter/corn-newsletter/2016-36/corn-testing-positive-vomitoxin-how-reliable-was-sampling.