Veterinary advice should be sought before applying any treatment or vaccine.


Mycotoxicosis refers to a number of different syndromes resulting from ingestion of feed, hay, supplements, by-products, or certain pasture plants that are contaminated with mycotoxins. Mycotoxins are toxic secondary metabolites produced by filamentous fungi. Not all mycotoxins are toxic, however the major mycotoxins that adversely affect horses include aflatoxin B1(AFB1), fumonisin B1, deoxynivalenol(DON), zearalenone (ZEA), and ochratoxin A (OTA). Fusarium, Aspergillus, and Penicillium are the most abundant molds that produce these toxins and contaminate grains used in feeds through fungal growth prior to and during harvest, or during (improper) storage of feed---either during transport, storage in feed stores, or in stable feed rooms. Heat-processing and ensiling do not destroy mycotoxins.

Cool, wet weather favors growth of Fusarium toxins, while hot, humid weather encourages aflatoxin formation. In the United States, Fusarium toxins are more prevalent in the Northeast and Midwest, while aflatoxins produced by Aspergillus are more common in the South.

Mycotoxins can cause acute poisoning if a large amount are consumed in a short period of time, and chronic poisoning if small amounts are ingested over an extended period of time. Mycotoxicosis severity depends on the amount consumed, duration of exposure, type of particular mycotoxin ingested, health status, and age of the horse.

Testing feed for Mycotoxins

Mycotoxins are invisible, odorless and cannot be detected by smell or taste. The only way to confirm the presence of mycotoxins is by mailing a sample of the feedstuff in question to a diagnostic laboratory that offers specific testing for mycotoxins in feed. There are basically two major types of mycotoxin tests that are available---quick tests and confirmatory or quantitative tests. Many laboratories doing confirmatory tests may initially run quick tests to determine whether the samples are positive and need further quantitative testing. Costs for mycotoxin tests vary for both kinds of tests. Quick tests may range from $10-$50 per sample, where confirmatory tests usually cost $75-$150 per sample, depending on the methods used and the number of mycotoxins included in the panel. Confirmatory testing from some laboratories may require up to 10 days from when they receive the submission until a report is generated.

Mycotoxin testing is offered at the following laboratories:


Decreased feed intake/feed refusal
Head pressing
Profuse sweating
Behavior changes


  • History
  • Clinical signs
  • Physical exam
  • Laboratory testing of feedstuff



Supportive care
Removal of suspected contaminated feed source


  • Always properly store feed in a closed, air tight container
  • Always check each bag of feed for contamination of mold, insects, or rancid appearance prior to feeding to horses. If it looks suspicious, trust your instinct and get a second opinion.

Scientific Research

General Overviews

Risk Factors

  • Buying poor quality feed
  • Recent change in feed
  • Hot, humid climate conditions
  • Improperly storing feed



Causative agent