Strategies For Handling Scabby And Vomitoxin-Affected Wheat Grain

Jun 29, 2015

By Stephen Wegulo

Extension Plant Pathologist

And Effects of Vomitoxin (DON) on Human and Animal Health

Excessively wet weather this spring favored development of Fusarium head blight (scab) in Nebraska wheat fields. The most severely affected fields are in the southeastern, south central, and southwestern parts of the state. The disease, caused mainly by the fungus Fusarium graminearum, is characterized by premature whitening or bleaching of wheat heads (Figures 1 and 2).

Wheat field with Fusarium head blight (scab)

Figure 1. A wheat field with severe Fusarium head blight in southeast Nebraska in 2015.

Figure 2. Close-up of a wheat head bleached by Fusarium head blight.

Bleached spikelets are sterile or contain kernels that are shriveled and/or appear chalky white or pink (Figure 3), referred to as Fusarium-damaged kernels, scabby kernels, or tombstones. Scabby grain usually contains the mycotoxin deoxynivalenol or DON, also known as vomitoxin. It belongs to a class of mycotoxins known as the trichothecenes. Scabby grain can also contain, to a lesser extent, the mycotoxin zearalenone. These mycotoxins are harmful to humans and animals.

This article outlines the effects of DON on human and animal health and strategies for harvesting and handling grain from fields affected by Fusarium head blight.

Effects of DON on Human and Animal Health

In humans, food poisoning characterized by diarrhea, nausea, vomiting, abdominal pain, headache, dizziness, and fever has been associated with consumption of Fusarium-infested cereals or food products. Trichothecenes have multiple effects on eukaryotic cell functions. The primary effect is believed to be inhibition of protein synthesis. DON can cause significant harm to humans and animals when ingested in large quantities. It has been shown to inhibit the absorption of certain nutrients by human intestinal epithelial cells. In animals, clinical signs of trichothecene toxicosis include feed refusal and weight loss, emesis, hemorrhage, and cellular necrosis of mitotically active tissues such as the intestinal mucosa, skin, and bone marrow. DON has not been reported to cause cancer. However, other mycotoxins that may be present in DON-contaminated grain can cause cancer. In addition, inhaling contaminated grain, chaff, or dust can cause allergic or respiratory reactions.

Scabby wheat grain compared with healthy wheat grain

Figure 3. Scabby wheat grain (left) and healthy grain.

Recommendations for Harvesting Fusarium-Infected Wheat

Harvesting. Increasing the fan speed on the harvest combine can remove some of the heavily infected grain, which usually is lighter and contains higher levels of DON than healthy grain.

Keeping Scabby Grain Separate. Consider keeping grain from heavily affected fields or parts of fields separate. Incidence and severity of scab varies from field to field and within a field depending on the variety planted and local environmental conditions.

Testing for DON and Zearalenone. Presence of scabby grain does not necessarily indicate high mycotoxin levels and vice versa. Therefore, consider testing grain from affected fields for DON and zearalenone content. The sample submitted for mycotoxin testing should represent the entire truckload or bin of grain.

Cleaning. If the proportion of scabby grain is high, consider cleaning the grain with seed cleaning equipment to remove or reduce scabby kernels. Cleaning does not eliminate DON as apparently healthy grain can have elevated concentrations of the mycotoxin. However, it significantly reduces levels of the mycotoxin by removing lighter, more heavily infected kernels.

Protecting Workers. When handling grain, wear appropriate personal protective gear to prevent inhaling mold spores and grain and chaff dust which can cause allergy and breathing problems. A two-strap, NIOSH-approved 95N or 100N respiratory mask is recommended. Wear latex/nitrile gloves to prevent skin absorption of DON and other mycotoxins that may be present in grain, chaff, or dust.

Storing Affected Grain. Scabby grain should be stored at or below 12% moisture content. This will reduce the potential for deterioration during storage. Cool the grain by aeration soon after placement in storage and continue cooling periodically as outdoor temperatures decline until the grain is at approximately 25°F.

Marketing. If possible, DON-affected grain should be kept separate from healthy grain. The marketing strategy for DON-affected grain will be influenced by many factors including DON levels, cleaning and/or blending costs, and contract obligations with elevators. In general, elevator discounts are highest at harvest and increase with the concentration of DON above 2 ppm. Therefore, weigh the pros and cons, including economics, of deferring DON-affected contracted wheat in the hope that discounts will reduce with time. Deferring delivery also gives time to clean and/or blend the wheat to improve quality.

Using Scabby Grain as Seed. To prevent or reduce damping off and seedling blights, scabby grain should be thoroughly cleaned and treated with a systemic fungicide before being used as seed for next season's crop.

Feeding. Scabby or DON-affected grain can be used as livestock feed. For recommendations on using feed contaminated with DON or zearalenone, consult the UNL extension publication Fusarium Head Blight of Wheat (EC1896). Straw from scabby fields can contain DON at concentrations that exceed 2 ppm. Therefore, straw from scabby fields should be tested for DON before using it for silage or bedding.

Advisory Maximum Levels for DON

A. 1 ppm DON on finished wheat products, e.g., flour, bran, and germ that may potentially be consumed by humans. FDA is not stating an advisory level for wheat intended for milling because normal manufacturing practices and additional technology available to millers can substantially reduce DON levels in the finished wheat product from those found in the original raw wheat. Because there is significant variability in manufacturing processes, an advisory level for raw wheat is not practical.

B. 10 ppm DON on grains and grain by-products (on an 88% dry matter basis) and 30 ppm in distillers grains and brewers grains (on an 88% dry matter basis) destined for ruminating beef and feedlot cattle older than four months and ruminating dairy cattle older than four months, with the added recommendations that the total ration for ruminating beef and feedlot cattle older than four months not exceed 10 ppm DON, and the total ration for ruminating dairy cattle older than 4 months not exceed 5 ppm DON. For chickens, 10 ppm DON with the added recommendation that these ingredients not exceed 50% of the diet of chickens. The total ration includes grains, all grain by-products including distillers and brewers grains, hay, silage, and roughage.

C. 5 ppm DON on grains and grain by-products destined for swine with the added recommendation that these ingredients not exceed 20% of their diet.

D. 5 ppm DON on grains and grain by-products destined for all other animals with the added recommendation that these ingredients not exceed 40% of their diet.

Source: unl.edu