Aflatoxin Still A Cautious Concern to Dairy Producers

By, Jenn Bentley, Dairy Field Specialist

As we move into post-harvest season and into storage of grain, the concern for aflatoxin issues can still be a concern to the dairy industry.  Dairy producers utilize many corn products in the cow’s ration and it’s important to know proper management practices in drought conditions that most of Iowa faced this year. 

What is aflatoxin?

Aflatoxins are a group of chemicals produced by certain mold fungi.  These fungi, Aspergillus flavus and Aspergillus parasiticus, can be recognized by olive green or gray-green, respectively, on corn kernels, in the field or in storage.  While four specific aflatoxins are generally produced (B1, B2, G1, G2), the most frequent and toxic is aflatoxin B1.

Why are we concerned?

Aflatoxin M1 contamination of milk results primarily from the conversion of aflatoxin B1 that is metabolized by enzymes found primarily in the liver.  After aflatoxin M1 is formed, it is excreted in the urine and milk of the cow.  Because aflatoxins are carcinogenic to animals and possibly humans, they are monitored closely in the food supply.  Most commonly, aflatoxin reduces the feed efficiency and reproduction of livestock. It can also suppress the cow’s immune system, leading to more frequent occurrence of infectious diseases.

Where might I find aflatoxin and why?

Aflatoxin B1 in feed is a mycotoxin produced by Aspergillus molds that grow on grain.  Corn in the field that has been subjected to high temperatures, prolonged drought, and high insect activity, is more susceptible to aflatoxin contamination.  Most frequently, aflatoxins are found in corn, corn silage, fuzzy cottonseed, and/or corn by-product feeds.  Corn distiller’s grain will be three times higher than the original corn in aflatoxin.

What conditions in storage enhance it post-harvest?

Aflatoxin can be produced in standing grain before harvest.  If conditions of moisture and temperature support continued mold activity after harvest, aflatoxins can continue to be produced during storage, especially at moisture content above 12% and temperatures greater than 700F.  Aflatoxin, once produced, is quite stable to heat, milling, pelleting, and many chemicals. 

What are the legal limits in milk and is it being tested for?

When aflatoxin is found in milk at concentrations of 0.5 ppb (parts per billion) or greater, the milk is discarded because it can’t be consumed for human consumption.  Cows that consume feed containing 20 ppb aflatoxins or greater may produce milk that exceeds the tolerance level.  Generally, all corn processed at a feed mill or mixed in a total mixed ration for dairy cattle should be scanned with a black light for aflatoxins.  It usually takes the cow 2-3 days on aflatoxin-free feed for milk concentrations to fall below tolerance levels.  This is highly dependent on the concentration of aflatoxins in the feed (and milk) as well as the diet being fed to the cow.  The Iowa Department of Agriculture and Land Stewardship has ordered milk processors to screen all Grade A and Grade B farm bulk milk pickup tankers and farm can milk loads for aflatoxin on a weekly basis.

How and where do I test for it?

Testing is the only certain way to know your risk.  There are simple, fast, semi-quantitative tests which can be performed to test for aflatoxin.  Kits using ELISA technology are available to test on the farm as well as commercially.  The antibody is also attached to a molecule that glows (fluoresces); if the fluorescence is read optically, then a quantitative (actual ppb) value can be determined. If the color change is just visual at a certain level, then a qualitative (yes or no) value above the preset threshold of the kit is determined and further testing is required.  The USDA GIPSA has evaluated and approved test kits for various toxins.  

Many buyers prefer to use off-site labs for testing; this is also true for crop insurance settlements where the adjuster has taken a sample on which to base the settlement.  A list of labs in Iowa is available at  USDA-GIPSA grading agencies, as well as several private labs and

 Iowa State University Veterinary Diagnostic Lab can do toxin testing on submitted samples. 

Strategies to deal with or mitigate aflatoxin issues:

  • If milk is found to be high in aflatoxin, it is critical that records be maintained of all feeds, feeding practices, milk quantities, contamination levels, as well as animal health and performance.  All grain products should be removed and replaced with new grain or related feeds in the diet that contain less than 20 ppb aflatoxin.  The removed feeds should then be tested to determine aflatoxin levels, particularly corn and cottonseed. 
  • Consider feeding the contaminated grain to other animals with higher tolerance levels.
  • Have your milk coop monitor your milk weekly to be sure it’s safe.
  • If the level of milk contamination exceeds 0.5 ppb on a second test, a special dietary chemisorbent should be added to the diet at recommended levels.  These compounds include clays (bentonite) and a yeast cell wall extract (glucomannans).  Mold inhibitors, such as organic acids, can prevent continued mold growth where moisture above 12-14% is a problem.  Mold inhibitors prevent A. flavus growth, but do not destroy or modify aflatoxins.
  • Treatment of grains with anhydrous ammonia for 12-14 days reduces aflatoxin content, but regulations vary from state to state about the clearance of ammoniation for contaminated corn.  Ammoniation is not yet cleared for commodities that would move in interstate shipment.  There are also human health dangers when handling and treating grains with anhydrous ammonia. 
  • Purchase ingredients that are relatively free of mycotoxins, be very cautious in purchasing of corn products during drought conditions.
  • Store grains at moisture levels less than 14%.
  • Clean up around the feed mill or feed troughs to eliminate damp areas suitable to mold growth. 
  • Clean equipment after harvest to avoid contamination
  • Particular caution should be applied to corn and corn silage stored in bags or vertical silos, since these feeds can make up a large portion of the diet and these storage structures will have as much variation in contamination as the fields from which they were harvested. 
  • Screen out fines and broken kernels as these are more susceptible to mold growth.


In summary, mycotoxin is found most commonly in pre-harvest grains that are harvested under drought conditions.  Conditions and storage post-harvest could amplify the issue, making it critical to manage all purchased and harvested commodities.  If the grain is found to have a concentration of 20 ppb aflatoxin or milk is tested above 0.5 ppb aflatoxin, the grain should be replaced.  In all cases, the grains should be tested for levels of aflatoxin.


Visit: more information on aflatoxin issues or other drought concerns.



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