Attention! This is a potentially life-threatening condition for your horse. Time is of the essence, contact your veterinarian immediately.Find a Vet


Aflatoxin Toxicosis, Aflatoxin Poisoning

Aflatoxicosis is the poisoning that occurs from ingesting aflatoxins. Aflatoxins are naturally occuring mycotoxins produced by the fungi Aspergillus flavus and A. parasitus.
There are over 20 types of aflatoxins, although the four major types are designated as B1, B2, G1 and G2. Aflatoxin B1 is the most dangerous. Aflatoxin B1 acts as a cytotoxin and class one carcinogen, causing damage the horse's liver, interfering with the RNA and protein synthesis and suppressing the immune system.

Horses can develop two types of aflatoxicosis, depending on the amount of toxin ingested and extent of exposure. Horses can develop acute or chronic form of aflatoxicosis, with the chronic form being the most common. Horses with chronic aflatoxicosis may exhibit subtle signs at first, including weight loss or decreased weight gain and poor haircoat. Signs may progress to depression, loss of appetite, jaundice (yellowing of mucous membranes), and eventually liver failure. Horses suffering from acute aflatoxicosis may demonstrate loss of appetite, depression, diarrhea, ataxia and signs of liver damage.

A. flavus is found in soil, crops, and stored animal feed. Since most horse feeds contain corn, oats and other cereal grains, they are susceptible to aflatoxin contamination. Horse feed is at a higher risk of developing aflatoxins if it isn't stored correctly and exposed to ambient temperatures between 78-90°F (25.5-32°C), and relative humidity between 97 - 99%.

It is suggested that horses with previous low level exposure to aflatoxins may develop an increased resistance to the cytotoxic effects of AFB1. It is also thought that there is a possible link between recurrent airway obstruction (RAO) and inhaled mycotoxins. Horses are exposed to mycotoxins from inhalation of contaminated feed-dust or hay particles.


Yellow mucous membranes
Loss of appetite
Brown urine
Poor haircoat
Increased heart rate
Increased respiratory rate
Rapid weight loss


  • History
  • Clinical signs
  • Physical exam
  • Blood testing - for anemia, elevated liver enzymes, serum bile acids, albumin:globulin ratio; prothrombin activity
  • Mycotoxin testing of feed

While waiting for your veterinarian

  • Remove suspected feed source from horse access


Supportive careFor resulting liver damage
Supplemental vitaminsL-methionine and Vitamin E


  • Supplemental antioxidants may help offset the toxic effects of the toxins

Scientific Research References

Good Overviews