Use of Feed Contaminated with Fungal (Mold) Toxins (Mycotoxins)

The purpose of this NebGuide is to provide guidelines on use of mycotoxin-contaminated feeds.

Michael P. Carlson, Diagnostic Toxicologist/Analytical Chemist
Steve M. Ensley, Veterinary Toxicologist

Mycotoxins are chemicals produced by fungi (molds) under certain conditions. They are not essential for fungal growth or reproduction, and they are toxic to animals or humans. They are naturally occurring chemicals found in grains, food and feed consumed by humans and animals that cannot be completely avoided. Accordingly, we try to control the amount of such chemicals ingested by humans and animals.

Mycotoxins commonly found in grains or feeds used in Nebraska are aflatoxins, ergot alkaloids, fumonisins, vomitoxin and zearalenone. Information about their health effects, diagnosis, and treatment may be found in NebGuide G1513, Understanding Fungal (Mold) Toxins (Mycotoxins). Information about sampling and analyzing grains or feed for mycotoxins may be found in NebGuide G1515, Sampling and Analyzing Feed for Fungal (Mold) Toxins (Mycotoxins).

Use of Mycotoxin-Contaminated Feeds

It is always safest not to use mycotoxin-contaminated or moldy feed. Even if no detectable amounts of known mycotoxins are present in such feed, unknown or uncharacterized mycotoxins may be present which cannot be detected using existing analytical methods. If mycotoxin-contaminated or moldy feed must be used, feed it to animals that are less sensitive to potential adverse health effects of mycotoxins.

There are many different kinds of mycotoxins belonging to many different classes of chemicals. It is difficult, if not impossible, to generalize about the sensitivity of dif­ferent species to adverse health effects caused by ingestion­ of mycotoxins. But ruminants are generally among the least sensitive to mycotoxins.

U.S. Food and Drug Administration (FDA) can establish limitations for concentrations of mycotoxins in animal and human foods. Limitations are labeled using different terms, including “action levels” for aflatoxins, “guidance levels” for fumonisins, and “advisory levels” for vomitoxin. USDA Federal Grain Inspection Service has set standards defining ergoty barley, mixed grains, oats, rye, triticale and wheat. The legalities of such designations and their application to animal production are beyond the scope of this NebGuide. The authors recommend that grain, feed and animal producers adhere to those limitations as much as possible.

Limitations placed on mycotoxins in feed are listed in Table I. If federal agencies have not established limitations for a mycotoxin, then we have listed recommendations for limitations found in a published reference. References are listed for all mycotoxins included in the table.

Blending Feeds to Reduce Mycotoxin Concentrations

Blending contaminated feed with uncontaminated feed to reduce mycotoxin concentrations is regulated by federal agencies. Blending food or feed containing a substance in excess of a limitation established by a federal agency may not be permitted. Blending aflatoxin-contaminated commodities is not permitted. The final product produced by blending may be unlawful, regardless of the concentration of the mycotoxin attained by blending.

Under certain circumstances, U.S. FDA may not object to blending feeds containing mycotoxins at concentrations higher than a limitation. In the case of aflatoxin in Nebraska corn harvested in 2002, the State Department of Agriculture requested permission from the U.S. FDA to blend corn containing aflatoxin under certain circumstances. Limitations were placed on uses for the blended products, however. Limitations applied to feed blended for marketing or for use by the grain producer. Before you blend mycotoxin-contaminated feed, contact the State Department of Agriculture for additional information.

If mycotoxin-contaminated feed is to be blended, then mycotoxin content of the uncontaminated and contaminated feeds must be known. Hopefully, the content of the uncontaminated feed will be very low. The following formula can be used to calculate the percentage of contaminated feed in the blended feed to achieve a specific mycotoxin concentration:

F = 100 x (C - L)/(H - L)

where F = fraction of contaminated feed in the final blend expressed as a percentage, C = desired mycotoxin concentration in the final blend, L = mycotoxin concentration in the “uncontaminated” feed, H = mycotoxin concentration in the contaminated feed. H must be greater than L.

For example, say corn was available contaminated with zearalenone at 10 ppm and is to be mixed with corn containing no detectable amount of zearalenone (detection limit 0.5 ppm) to a concentration of no more than 1 ppm. Using the formula to calculate F: C = 1 ppm, L = 0.5 ppm (safer to use the detection limit concentration than to assume there is no zearalenone in the uncontaminated corn), H = 10 ppm. Plugging the numbers into the equation and performing the calculations:

F = 100 x (1 - 0.5)/(10 - 0.5) = 100 x (0.5/9.50) = 5.26%

Since we want the blended grain to contain no more than 1 ppm, it would be better to round F down to 5 percent, so the blended grain should not contain more than 5 percent contaminated corn.


Anonymous (2000) Action Levels for Poisonous or Deleterious Substances in Human Food and Animal Feed, US EPA Industry Activities Staff Booklet (www.cfsan.fda.gov/~lrd/fdaact).

Code of Federal Regulations (CFR), Title 7, Section 810 - Agriculture, Official US Standards for Grain, Jan 1, 2001 (www.access.gpo.gov/nara/cfr/cfr-table-search.html).

Guidance for Industry: Funmonisin Levels in Human Foods and Animal Feeds, US FDA, Center for Food Safety and Applied Nutrition, Center for Veterinary Medicine, Nov 9, 2001 (www.cfsan.fda.gov/~dms/fumongu2.html).

Osweiler, G.D. (1996) Toxicology, The National Veterinary Medical Series, Williams & Wilkins, Media, PA: 409 ff.

US Department of Agriculture (USDA) Grain Inspection, Packers and Stockyards Administration (GIPSA) Backgrounder - Deoxynivalenol (DON), November 2001. (www.usda.gov/gipsa).

US Federal Drug Agency (FDA), Office of Regulatory Affairs (ORA) Compliance Policy Guides (CPG) 7126.33 Sec. 683.100 - Action Levels for Aflatoxin in Animal Feeds, Issued Nov 21, 1979, reissued Oct 1, 1980, Revised Aug 15, 1982, May 18, 1989, and Aug 28, 1994 (www.fda.gov/ora/compliance_ref/cpg).

Table I. Action or recommended maximum concentrations of mycotoxins in animal feeds.
in diet
(action levels)
Corn, peanut products,
other feeds or feed

Finishing (feedlot) beef cattle

Breeding beef cattle, breeding
swine, mature poultry

Finishing swine > 100 lb

300 ppb

100 ppb

200 ppb

Policy Guides
Sec 683.100
Corn, peanut products, or
other feeds or feed ingredients,
excluding cottonseed meal
Immature animals 20 ppb
Cottonseed meal Beef, cattle, swine, poultry
(regardless of age)
300 ppb
All feeds or feed
Dairy animals, animal species not
listed above, uses not listed above,
intended use unknown
20 ppb
Ergot Barley Standards define ergoty grain products
under federal grain quality regulations.
They are not listed by animal species.
< 0.1% ergot sclerotia Some references indicate
adverse health effects
may occur at concentrations
beginning at 0.1% in the diet.
7 CFR 810
Mixed grain Predominately wheat or rye:
< 0.3% Other mixed grains:
< 0.1%
Oats < 0.1%
Rye < 0.3%
Triticale < 0.1%
Wheat < 0.05%
Corn and corn
Equids (horses) 5 ppm (< 20%
of diet)
Nov 9, 2001
Swine and catfish 20 ppm
(< 50% of diet)
Breeding ruminants, breeding poultry,
lactating dairy animals, laying hens
30 ppm
(< 50% of diet)
Ruminants > 3 months old, raised
for slaughter
60 ppm
(< 50% of diet)
Poultry raised for slaughter 100 ppm
(< 50% of diet)
All other species or classes
of livestock
10 ppm
(< 50% of diet)
(advisory levels)
Grain and grain products Swine and other animal species,
except cattle and chickens
Swine: 5 ppm
(< 20% of diet)
Other species:
5 ppm
(< 40% of diet)
from 1982
and 1993
Ruminating beef and feedlot cattle
older than 4 months, chickens
10 ppm
(< 50% of diet)
Zearelenone Diet Prepubertal gilts < 1 ppm   Osweiler
(1996): 421
Sexually mature sows, bred sows < 3 ppm
Young boars < 20 ppm
Mature boars < 200 ppm
Virgin heifers < 10 ppm

This publication has been peer reviewed.

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Index: Plant Diseases
Issued June 2003