Aflatoxicosis in Horses

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

A Closer Look: What is 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. Symptoms include:

• Fever • Rapid breathing • Straining to defecate

• Blood in the feces• Seizures • Sudden death 

Uncoordinated movement (ataxia)

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

• Appetite loss • Weakness • Yellow gums and skin

• Head pressing • Circling

• Uncoordinated movement (ataxia)

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:

• Mild diarrhea

• Poor coat condition 

• Weight loss

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

Main symptoms of aflatoxicosis include 

• Lethargy 

• Excessive bleeding

• Tremors 

Uncoordinated movement (ataxia)

• Fever 

Yellow gums or skin

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

Steps to Recovery

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 Common in Horses?

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

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