wheat field

Molds and Fungi and Mycotoxins, Oh My!

By Dr. Gene P. Gengelbach, Ph.D., PAS

There has been a great deal of concern lately about mycotoxins in the 2016 grain and forage crops.  Many producers are surprised because, in many cases, yields were good and there is no visible mold in the corn or corn silage.  This article will discuss what mycotoxins are, where they come from, and what can be done to reduce their impact on the animals you are feeding.

Molds vs. Mycotoxins

  • Molds are fungi that can infect either the growing plant or a stored feedstuff.
  • Molds rarely infect animals, usually only when their immune systems are severely depressed.
  • Mycotoxins are toxic metabolites produced by molds (myco means fungus; toxin means poison)
  • There are hundreds of known mycotoxins; most labs analyze for only a few.
  • Not all molds produce mycotoxins
  • Mycotoxins can be formed in the field, in storage, or both.
  • Some molds produce multiple mycotoxins; some mycotoxins can be formed by several species of fungi.
  • Mycotoxin production is often associated with weather extremes or other conditions such as hail, wind, or insect damage that can stress the host plant.
  • Fusarium and Aspergillus species are some of the major mycotoxin producers.

Fusarium MoldsFusarium Mold pic

  • Fusarium (and related Gibberella) molds are whitish-pink molds that can infect the grains in the field (Fusarium ear rot and Gibberella stalk rot in corn, Fusarium head scab in wheat and small grains).
  • Fusarium molds can also grow on stored silage and high-moisture grains.
  • Spores overwinter in crop residue; enter the plant through silks, grain or stalk wounds.

Infection is more likely under cool, wet weather conditions during pollination and grain fill.

  • Major toxins produced are Deoxynivalenol (DON, more commonly known as Vomitoxin), Zearalenone, Fumonisins, T-2 toxin, and other Type A and Type B Trichothecenes.

Aspergillus Molds

  • Aspergillus molds are greenish-olive in color and can come from the field or in storage.
  • It grows best in hot, dry weather; occurs primarily in the Southern U.S. or further north in drought- or heat-stressed situations.
  • Aspergillus molds produce aflatoxin, which is the only toxin regulated by the U.S. Food and Drug Administration (FDA).
  • Aflatoxin is considered to be a carcinogen and is limited to 20 parts per billion (ppb) in dairy feeds and 0.5 ppb in milk.
  • Any feedstuff containing over 20 ppb aflatoxin CANNOT be fed to lactating dairy cows, even if blended with other feed or grains with lower levels of aflatoxin.
  • Besides grain, aflatoxin may be found in cottonseeds and peanuts.

General Symptoms of Mycotoxicosis

  • Reduced feed intake or feed refusals
  • Intermittent diarrhea/inconsistent manure due to gut irritation/inflammation
  • Reduced growth, performance, immune function
  • Irregular heats, reduced reproductive performance, precocious puberty; all due to Zearalenone which has a chemical structure very similar to the hormone estrogen
  • Ruminants are generally less sensitive to mycotoxins than non-ruminant animals because many toxins can be degraded in the rumen.
  • Beef is less sensitive than dairy animals because they have lower feed intakes and slower digestive rates of passage, giving more time for degradation of mycotoxins in the rumen.

Reducing the Risk of Mycotoxins

  • Reduce the amount of plant residue left on the surface of the field.
  • Rotate crops to break the disease cycle.
  • Prevent insect damage in the field and stored grain.
  • Dry stored grains to 14% moisture or below and properly aerate grain to prevent “hot spots” where mold can grow.
  • Harvest silage and high-moisture grains at the proper moisture level, pack well, cover promptly, and use the recommended amount of Silo-King®.
  • Consider fungicide use on standing crops.

Feeding Strategies When Mycotoxins are Present

  • Dilute mycotoxin-containing feedstuffs with “clean” feeds (except for aflatoxin as stated above).
  • Discard any moldy feed. Be careful where you spread it because you are inoculating the ground with mold spores for next year’s crop to deal with.
  • Make sure rations are properly balanced for optimum production, especially with regards to vitamin and trace minerals which help support immune function and general health. Direct-fed microbial products like Tri-Lution® help stimulate immune function as well.
  • Feed enzyme products such as Ru-Mend® or Zy-Mend® to increase nutrient availability.
  • Research studies have shown that clay-based products (including bentonite, montmorillonite, zeolite, hydrated sodium calcium aluminosilicates (HCAS) plus many others) do a good job of binding aflatoxins; their effect on other mycotoxins is variable.
  • Other compounds that have been studied in rations containing mycotoxins are charcoal, activated carbon, complex yeast cell wall polysaccharides, and specific enzymes designed to detoxify certain groups of mycotoxins.
  • There are NO products approved by the FDA for the binding or prevention of mycotoxins. Most of the products mentioned above are considered to be “flow agents”, pellet binders, or providers of certain nutrients, and cannot be labeled as mycotoxin binders.


Table 1.  Advisory levels of mycotoxins in livestock feed (FDA Compliance Program Guidance Manual)

Toxin Poultry Swine Dairy Beef
Aflatoxin, ppb Broilers      20

Layers    100

Growing      20

Breeding    100

Lactating     20 Breeding    100
Vomitoxin, ppm


Grain/Byproduct  10

Finished Feed    5

Grain/Byproduct   5

Finished Feed   1

Grain   5

Total Ration  2

Grain    5

Total Ration  10

Fumonisins, ppm Grain/Byproduct  100

Finished Feed    50

Grain/Byproduct 20

Finished Feed  10

Grain   30

Total Ration   15

Grain   60

Total Ration  30

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