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Key takeaways

Aflatoxins are a group of fungal toxins produced by Aspergillus fungi, which grows on a number of feed crops, such as corn, peanuts, and soybeans. 

  • Aflatoxicosis is a life-threatening fungal poisoning that occurs in horses as the result of ingestion of aflatoxins 
  • Once ingested, aflatoxins cause liver damage
  • Symptoms include appetite loss, tremors, uncoordinated movement, yellow gums or skin, and weakness
  • There is no specific antidote for aflatoxicosis
  • Treatment options are limited and include removal of contaminated feed and symptomatic and supportive care 
  • Prognosis depends on the severity of liver damage, the amount of toxin ingested, and timing of treatment
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A closer look: Aflatoxicosis in Horses

Aflatoxicosis symptoms can be divided into acute, subacute, and chronic forms:

Acute aflatoxicosis occurs when horses consume a single, large dose of toxin.

Subacute aflatoxicosis occurs when horses ingest a moderate dose of toxin over several days, causing rapid liver failure.

Chronic aflatoxicosis occurs when small amounts of toxin are ingested over long periods of time. Symptoms are typically mild and difficult to attribute to toxicosis.

Risk factors

Aflatoxicosis is rare in horses, but is more common in horses eating corn-based diets. Aflatoxicosis is a life-threatening fungal poisoning and must be treated as an emergency. Early detection and subsequent elimination of contaminated feed is the best way to ensure recovery.

Aflatoxins are found worldwide but are more likely to develop in humid and warm conditions.

Possible causes

Aflatoxicosis is caused by ingestion of feed contaminated with aflatoxins, produced by fungus growing on grain crops. Aflatoxin B1 is the most common and most toxic type of the aflatoxins, and can be found in a variety of staple feed components, such as:

  • Corn
  • Sorghum
  • Barley
  • Rye
  • Wheat
  • Peanut
  • Soya
  • Rice
  • Oats
  • Cottonseed

Main symptoms

Testing and diagnosis

Horses presenting with symptoms of aflatoxicosis generally undergo the following diagnostics:

  • Physical examination
  • Bloodwork
  • Urinalysis
  • Feed analysis
  • Liver biopsy
  • Ultrasound of the liver

Testing and diagnosis

The first step in treatment is preventing exposure to contaminated feed. Once the source of the toxin is removed, treatment is focused on supportive and symptomatic therapy, including:

  • IV fluids
  • Liver supporting supplements

No specific antidotes are currently available.

Prognosis of aflatoxicosis is dependent on the amount of toxin ingested and the degree of liver damage.

Acute and subacute cases of aflatoxicosis carry a poor prognosis, and most animals die due to severe liver damage or failure. Chronic cases have a guarded prognosis with supportive care, and often require long-term management and repeated bloodwork to monitor recovery.


While not contagious, lactating mares with known exposure to aflatoxins should not nurse their foals, as toxins can be passed through the mother's milk.

Prevention strategies include:

  • Buying feed from companies with rigorous quality control
  • Proper storage of feed in dry, cool places
  • Avoiding long-term storage of feed
  • When possible, analysis of feed before feeding

Is Aflatoxicosis in Horses common?

Aflatoxicosis is rare in horses. It is more common in corn-fed diets and places where the climate is warm and humid.

Typical Treatment

  • Supportive care
  • Removal of contaminated feed


Christopher Brown and Wilson Rumbeiha - Writing for Vetlexicon
Clair Thunes, PhD - Writing for The Horse
Michelle S. Mostrom , DVM, MS, PhD, DABVT, DABT - Writing for MSD Veterinary Manual
Gary D. Osweiler, DVM, MS, PhD, - Writing for MSD Veterinary Manual
Francesca Caloni and Cristina Cortinovis - Writing for The Veterinary Journal

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