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Aflatoxin was discovered in 1961 as the cause of “turkey X disease” and resulted in research leading to the discovery of mycotoxins. Aflatoxin is considered to be the mycotoxin of most concern to animal and human health. Aflatoxin naturally occurs in four forms: aflatoxin B1, B2, G1, and G2. Of these, aflatoxin B1 is considered the most potent naturally occurring carcinogen known. Unlike most toxins, the animal’s attempt to detoxify aflatoxin results in the production of metabolites that are still of concern and highly regulated. Aflatoxin B1 may also be converted to aflatoxin M1, which gets its name from its occurrence in milk. However, several commercial feed additives and sequestering agents have been tested and demonstrated to be effective at reducing exposure to aflatoxin from feed.

Species Producing Aflatoxin

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Aflatoxins are commonly produced by Aspergillus parasiticus and A. flavus. However, species of the genera Fusarium, Penicillium, Claviceps, and Alternaria may also produce aflatoxins.

Occurrence of Aflatoxin

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Aspergillus flavus is considered one of the most common storage molds, occurring worldwide. Aflatoxins thus are a global problem. Corn, peanut, and cotton are the commodities that primarily affect livestock, but other grains may be a source of aflatoxin. Contamination of corn silage and grain is problematic and is usually related to pre-harvest contamination of the corn plant. Incidence of drought, humidity, flooding, or insect damage may increase the presence of aflatoxin.

Regulation of Aflatoxin

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Because of its carcinogenic properties, aflatoxin is strictly regulated in both animal feed and milk and in human food. Aflatoxins in dairy feeds have an action level of 20 parts per billion (ppb), and aflatoxin M1 in milk has an action level of 5 ppb. Regulations vary based on feed and species. In the European Union, aflatoxin limits are regulated at 0.05 ppb.

U.S. Food and Drug Administration Action Levels for Aflatoxin in Human Food, Animal Feed, and Animal Feed Ingredients

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Commodity Action Level (ppb)
Corn and peanut products intended for finishing beef cattle in feedlots


Cottonseed meal intended for beef, cattle, swine, or poultry (regardless of age or breeding status)


Corn and peanut products intended for finishing swine of 100 pounds or larger


Corn and peanut products intended for breeding beef cattle, breeding swine, or mature poultry


Corn, peanut products, and other animal feeds and feed ingredients (excluding cottonseed meal, which is intended for immature animals)


Corn, peanut products, cottonseed meal, and other animal feed ingredients intended for dairy animals, for animal species or uses not specified above, or when the intended use is not known


Milk (aflatoxin M1)


Source: U.S. Food and Drug Administration, 2000.


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Aflatoxicosis is most often the result of exposure to small quantities of aflatoxin over a long period of time. This may be observed as reduced animal performance (reduced feed intake and milking performance). The immune system is inhibited, making the animals more susceptible to diseases and infections. Most often, aflatoxicosis is undetected and results in an economic loss associated with reduced production, but if animals continue to consume contaminated feed, aflatoxicosis will result in liver damage and could lead to death.


Skip to Sources

Diaz, D. The Mycotoxin Blue Book. 2005. 295–323. Nottingham, UK: Nottingham University Press.

U.S. Food and Drug Administration. 2000. Guidance for Industry: Action Levels for Poisonous or Deleterious Substances in Human Food and Animal Feed. Accessed Aug. 12, 2021.


Assistant Professor and Extension Specialist
Animal Science
Graduate Assistant
Animal Science
Graduate Assistant
Animal Science

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Publication date: Aug. 23, 2021

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