Moldy Sweet Corn Poisoning (Fumonisin Toxicity and ELEM) in Horses

Key Takeaways

Fumonisin toxicosis is a life-threatening condition that occurs when horses ingest fumonisin, a fungal toxin produced by Fusarium verticillioides or F. proliferatum fungi which grow on sweet corn. 

• Fumonisin can cause two separate syndromes: equine leukoencephalomalacia (ELEM) or liver damage

• Common symptoms include uncoordinated movement, blindness, circling, recumbency, and sudden death

• There is no antidote for fumonisin poisoning, and treatment options, which are limited, involve removal of contaminated corn as well as symptomatic and supportive care

• Even with treatment, most animals die after the onset of symptoms

A Closer Look: What is Fumonisin Toxicosis in Horses?

Fumonisin toxicosis is a rare condition in horses. It mainly affects animals that are fed corn-based diets.

Moldy sweet corn toxicosis is a life-threatening fungal poisoning and must be treated as an emergency. Once symptoms of fumonisin toxicosis develop, most horses have a guarded to grave prognosis.

Risk Factors

Moldy sweet corn poisoning in rare in horses. It is more common in horses on corn based diets. Horses living in humid and warm areas are at a higher risk of toxicosis.  

Moldy corn toxicosis can cause two separate syndromes:

Neurotoxic form: Equine leukoencephalomalacia (ELEM) is the most common form of fumonisin toxicosis. The ingestion of large doses of the toxin over a short period causes ELEM. Symptoms include:

• Lethargy • Circling • Head pressing 

Uncoordinated movement (ataxia) • Weakness 

• Blindness • Recumbency 

Hepatoxic form: rarer and generally occurs when small doses of toxin are ingested over an extended period. Symptoms include: 

• Swelling of the head and lower jaw 

Yellow skin (jaundice)

Red spotting on the gums

The two syndromes can occur concurrently or separately.

Possible Causes

Moldy sweet corn toxicosis is caused by the ingestion of corn contaminated with fumonisin, a fungal toxin produced by Fusarium verticillioides and F. proliferatum fungi. 

Fumonisin can be found in corn and corn-based products that become moldy as the result of excessive moisture.

Main Symptoms

The main symptoms of fumonisin toxicosis include:

• Lethargy • Circling • Reduced appetite

• Blindness • Head pressing • Recumbency 

Uncoordinated movement (ataxia)

• Increased responses to stimuli

• Drooping of the lip or ear • Loss of consciousness

Testing and Diagnosis

Horses presenting with symptoms of moldy sweet corn toxicosis generally undergo the following diagnostics: 

• Physical examination 

• Neurological examination 

• Cerebrospinal fluid analysis (spinal tap)

• Bloodwork

• Feed analysis 

• Liver biopsy

Steps to Recovery

The first step in treatment is removing contaminated feed. 

Once the source of the toxin is removed, treatment focuses on supportive and symptomatic therapy, including:

• IV fluids

• Activated charcoal to prevent further toxin absorption

• Medications to protect the liver

• Sedation

Note: always consult a veterinarian before administering medication, including activated charcoal.

No specific antidotes are available, and in the majority of cases, horses die as the result of fumonisin ingestion.

Most cases of fumonisin toxicosis carry a very poor prognosis, with most animals dying shortly after the onset of symptoms. 

In mild cases, the prognosis is guarded, and animals that are able to recover can suffer from lifelong neurological deficits.


Moldy sweet corn toxicosis is not contagious.

Prevention strategies include:

• Analyzing corn and corn-based products before feeding

• Proper storage of corn in dry places 

• Avoiding long-term storage of feed

Is Fumonisin Toxicosis Common in Horses?

Fumonisin toxicosis is uncommon overall, but is more common in horses that are fed corn-based diets.

Typical Treatment

• Removal of fumonisin source 

• Supportive and symptomatic care 

• No specific treatment

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