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


Mycotoxicosis refers to syndromes resulting from ingestion, skin contact or inhalation of mycotoxins. Mycotoxins are the secondary metabolites of molds belonging to several genera, including Aspergillus, Fusarium and Penicillium spp. Other genera include Alternaria, Chaetomium, Cladosporium, Claviceps, Diplodia, Myrothecium, Monascus, Phoma, Phomopsis, Pithomyces, Trichoderma and Stachybotrys. Studies show that mycotoxins contaminate 25% of the world's agricultural products each year. Agricultural products most affected include cereal grains (wheat, barley, millet, oats, peas, millet, corn), dried fruits, nuts, hay, pasture grasses and spices.
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).

Mycotoxin NameProduced byDescriptionAssociated Syndrome
Aflatoxins Aspergillus flavus, A. parasiticus, A. nomius and A. pseudotamarii.Among the various toxic mycotoxins, AFB1 is the most lethal, exhibiting harmful hepatotoxic, mutagenic, teratogenic and carcinogenic effects on many species of animals.Aflatoxicosis
FumonisinsFumonisn verticillioides and F. proliferatum.Most frequently found in corn (maize) and corn-based feeds. Fumonisin B1 (FB1) is the most commonly found and most thoroughly studied. The US FDA and European Union Commission have established guidelines for maximum levels of FB1 that horses can safely consume. Of all animal species, horses are the most sensitive to fumonisin toxicity. Onset of ELEM can occur as early as 7 days after a change in diet, but usually it takes 14-21 days until clinical signs appear. Usually multiple horses are affected---those consuming the same batch of feed.
equine leukoencephalomalacia (ELEM)
Ochratoxin A (OTA)Aspergillus ochraceus in warm climates) and Penicillium (predominately P. verrucosum found in temperate climates)Found commonly in cereal crops; however oats and wheat, as well as their by-products such as bran and middlings, are at the highest risk of contamination.
Trichothecenes (T-2 toxin, diacetoxyscirpenol, neosolaniol, nivalenol, diacetylnivalenol, deoxynivalenol (DON), HT-2 toxin, and fusarenon X)A common contaminate in corn and wheat and are responsible for causing digestive disorders, feed refusals, edema, dermatitis, oral lesions, hemorrhaging, and blood disorders.
Zearalenone (ZEA)Fumonisin graminearumFound most frequently in moldy hay, corn, and pelleted commercial feed. It causes problems with fertility and reproductive ability.
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. The symptoms of mycotoxicosis depend not only on the type of mycotoxin, but also to the relative amount and duration of exposure as well as the species, age, sex, health, environment, nutritional state and particularly for the interactions with other toxic insults.


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


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


Supportive care


  • 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 References

Good Overviews

Risk Factors

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



Causative agent