Expert Answers - Dec. 18, 2009

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Answer provided by Mike Hutjens, extension dairy specialist at the University of Illinois-Urbana.

Q: Why should we be concerned about moldy corn from the recent harvest?

A: Moldy corn reduces bushel weight, corn quality, nutrient content, and increases the risk of mycotoxin formation. Mycotoxins are toxic substances produced by fungi (molds) growing on grain or feed in the field and in storage. Mycotoxins associated with cool and wet conditions are deoxynivalenol (also called DON or vomitoxin), zearalenone, T-2 toxin, and fumonisin. Aflatoxin is another toxin, but is associated with hot weather and/or drought stress conditions. Diplodia ear rot is also present, but no toxins are associated with the condition.

Signs of mycotoxin in dairy cattle include immune suppression (cattle do not respond to disease challenges), rumen disorders and reduced microbial digestion, loose fecal discharges, reduced dry matter intake, decline in fertility and hormonal like changes (udder development and fertility).

Mycotoxin risk levels for dairy cattle are listed in Table 1 (expressed on a total ration dry-matter basis). Dilution with clean feed can reduce levels, but contaminated corn and corn silage can vary greatly in concentration. Note: Some toxins are listed as parts per billion; others are parts per million.

Table 1. Suggested maximum levels of mycotoxins for lactating dairy cows (expressed on a 100 percent dry-matter basis in the total ration)

DON (vomitoxin)

< 5 to 6 parts per million

Fumonisin < 25 ppm million
T-2 toxin < 100 to 200 parts per billion
Zearalenone < 300 parts per billion
Aflatoxin < 20 parts per billion

If you are concerned that mold risks could be a problem, the following guidelines may be helpful:

  • Testing for mycotoxins can provide an estimation of risk. Tests can be expensive and sampling and feed variation can reduce the usefulness of the results. Results from a Midwest testing lab are listed in Table 2 for your reference.

Table 2. Levels of mycotoxin in feed from Oct. 1, 2009 to Dec. 3, 2009 (Source: Dairyland Labs)



Samples Tested (number) Positive (% of total) Over-target values (% based on Table 1)
Corn Vomitoxin 485 77 4
  Zearalenone 440 48 5
  Aflatoxin 297 9 0
  T2 204 25 0
Corn silage Vomitoxin 91 60 10
  Zearalenone 52 35 37
  Aflatoxin 44 7 0
  T2 31 0 0
  • Adding a mycotoxin-binder can reduce the impact of toxins be reducing their impact in the digestive tract and/or not absorbed. (Binders include yeast cell wall extracts or MOS products and clay binders.)
  • Drying wet corn below 15 percent moisture stops further toxin development in storage.
  • Young animals and pregnant cattle are at higher risk, while steers can tolerate higher levels.
  • Removing fines, damaged seeds and cracked corn kernels can reduce toxin risk.
  • If you purchase corn screenings, higher levels of mycotoxin risk can be present.
  • Distillers grain produced from ethanol production can concentrate the level of toxins in the original corn used; know your sources of distillers grain.

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