Understanding Mycotoxins



Mycotoxins are toxic products of fungal metabolism which occur in a wide variety of substances including animal feed and human food. Mycotoxins can cause human health problems and economic losses in livestock. The mycotoxins that are of significance in animal feeds are; aflatoxin, fumonisin, and the fusarial toxins (vomitoxin, zearalenone and T-2 toxin).



Aflatoxin is the most potent, naturally occurring carcinogen known to man. Aspergillus flavus and Aspergillus parasiticus are the two molds that are the major producers of aflatoxin. These two fungi are found everywhere in the world. They are soil-borne but have an affinity for the rich growth media provided by seeds. These toxins are produced pre-harvest in the field and post-harvest in storage. Insect damage, mishandling or weather stress assists the fungi in invading the seed. These fungi require a temperature over 75°F and moisture greater than 14% to grow. It has been determined that both fungi thrive in environments where the temperature is between 70° and 100°F and the moisture level is between 14% and 30%. A closed, poorly ventilated condition creates an ideal environment for these fungi to grow.

Aflatoxins have been detected in corn, peanuts, wheat, rice, cottonseed, tree nuts, milk, eggs, cheese, copra, milo and other foods.

Animals affected by aflatoxins include: cattle, sheep, chickens, pheasants, turkeys, ducklings, quail, swine, dogs, cats, fish, laboratory animals, monkeys and humans.

If an animal consumes a feed that is contaminated with aflatoxin, many health and performance problems may develop. Most commonly these animals display poor performance, such as reduced feed intake, decreased feed efficiency/weight gain, decreased milk production and decreased resistance to infection. Aflatoxin may suppress an animal's immune system, resulting in diseases that may be diagnosed as the cause of poor performance, when in fact the aflatoxin has caused the disease/poor performance. Some effects of aflatoxin ingestion that have been documented are liver damage, kidney and intestinal hemorrhage, and liver tumors. Substantial physical and economic loss can result in feeding livestock and poultry aflatoxin contaminated feed.

Aflatoxin can also be metabolized by dairy animals, resulting in contaminated milk and dairy products.

The United States Food and Drug Administration (FDA) has set regulatory levels for commodities containing aflatoxin. These levels vary depending on the use of the commodity. If a commodity is intended for use in human food, feed for immature livestock and poultry, feed for dairy animals, or its destination is unknown, the FDA enforcement level for aflatoxin is 20 ppb (parts per billion.) If the commodity is intended for use for breeding cattle, breeding swine, mature poultry (including laying hens), it may contain no more than 100 ppb aflatoxin. If the commodity is intended for feeding finishing swine (weighing 100 pounds or more), it may contain no more than 200 ppb aflatoxin. The maximum allowed level for finishing beef cattle is 300 ppb.



Vomitoxin is classified as a fusarial toxin, a toxic metabolite of the Fusarium mold family. Toxins also produced by the Fusarium molds include zearalenone and T-2 toxin. Vomitoxin and zearalenone may occur together, especially in scabby wheat and in giberella ear rot of corn.

Fusarial toxins have been detected in corn, wheat, bran, rice, cottonseed, midds, milo, flour, barley, malt, beer and other foods. Species affected by these toxins include humans, cattle, swine, chickens, pheasant, turkeys, duckling, quail, dogs, sheep, cats, monkeys, fish and laboratory animals.

Vomitoxin can cause wheat products to have an "off flavor." FDA evidence indicates a link of acute gastrointestinal illness in humans with the ingestion of vomitoxin. When it contaminates a feed ingredient, vomitoxin can produce vomiting, feed refusal, immune suppression, diarrhea, weight loss and/or milk production losses in dairy cattle. Pigs are extremely sensitive to vomitoxin. Levels as low as 0.5 ppm has been reported to cause palatability problems in swine rations, resulting in economic losses. Actual problem levels of vomitoxin vary from animal to animal. The age and overall health of the animal have an affect on how an animal may respond to the ingestion of vomitoxin.

Affected animals may rebound when the contaminated feed has been removed.

FDA has established advisory levels for vomitoxin. These levels are as follows:


  • Humans 1 ppm Wheat*, Barley* (*finished products)
  • Cattle, Chickens 10 ppm All Grains & Grain
    • (not to exceed by-products < 50% of diet)
  • Swine 5 ppm All Grains & Grain
    • (not to exceed by-products < 20% of diet)
  • All other animals 5 ppm All Grains & Grain
    • (not to exceed by-products < 40% of diet)



Fumonisin, like vomitoxin, is a toxic metabolite of the Fusarium mold family. Fumonisin is produced by the molds Fusarium moniliforme and Fusarium proliferatum which are soil borne fungi. These fungi grow rapidly from single cell spores into the thread-like masses that produce fumonisin.

Fumonisin is found primarily in corn and corn-based products. Corn screenings can be a source of high levels of fumonisin. There are several chemical forms of fumonisin. Fumonisin B1, B2 and B3 are the types of most concern. Fumonisin is generally produced in warm to hot climates. Fusarium moniliforme has been found in corn kernels grown where there is good nutrition and water. The mold spores can infect developing ears of corn or harvested crop in storage.
Fumonisin ingestion affects different animals in different ways. Humans, horses, cattle, swine, poultry, mice, rats and rabbits have been found to be affected by fumonisin. Research is being conducted to determine whether other animals may be affected and in determining risk levels in all species.

Horses are extremely sensitive to fumonisin. Very low concentrations can cause leukoencephalomalacia (ELEM) or liquefication of the brain. It is also known as "crazy horse disease" and "the blind staggers." Affected horses display symptoms such as blindness, head butting and pressing, constant circling and ataxia, followed by death. In swine, fumonisin attacks the cardiopulmonary system, causing pulmonary edema and liver and pancreatic lesions. Fumonisins have been linked to cancer in humans.

Fumonisin can occur in any geographic location where corn is grown. It is considered to be prevalent in corn. Higher concentrations can occur when conditions are favorable. Since 1994, outbreaks of fumonisin contaminated corn have been reported in Arizona, Indiana, Kentucky, North Carolina, South Carolina, Texas and Virginia.

Testing corn products for fumonisin is the best way to ensure that the final feed product has no/low levels of fumonisin. Grain contaminated with fumonisin levels higher than 50ppm are usually blended or destroyed. The molds that produce fumonisin can be destroyed in food and feed, but the toxin, which is responsible for the illnesses, cannot be removed from the product. To help prevent mold and toxin formation, feed should be kept fresh. Leftover feed should be removed from bunks and mangers before fresh feed is added. Spraying of newly exposed silage with propionic solutions after removing silage from bunker silos each day has been demonstrated to help retard heating and mold development.

FDA has yet to establish advisory levels for fumonisins in corn (finished product and/or starting corn.) The American Association of Veterinary Laboratory Diagnosticians (AAVLD) has established advisory levels for fumonisin. These levels are as follows:


  • Horses (non-roughage portion)
  • Swine (total diet)
  • Beef Cattle (non-roughage portion)
  • Poultry (total diet)
  • (Data is currently being collected to determine safe levels for human and dairy cattle consumption.)