Leukoencephalomalacia in Horses

An uncommon disease of the central nervous system, equine leukoencephalomalacia (ELEM), also known as equine mycotoxic encephalomalacia and moldy corn poisoning, can cause serious issues in the horses affected by it. This illness occurs when a horse eats feed or hay that is contaminated with fumonisin mycotoxins. The Food and Drug Administration in the U.S. has developed regulatory limits for the fumonisin levels that can be in feed, corn and corn byproducts that are meant for consumption by horses; feed that is contaminated cannot make up more than 20% of a horse’s diet. 

The condition can show as soon as seven days after a change in the diet of your horse, though it will more likely take 14-21 days until symptoms appear. It will usually occur in more than one horse, happening to those who ingest the same batch of feed. Unfortunately, the condition is hard to diagnose in horses and often leads to sudden death, sometimes without any symptoms. The majority of the damage will take place in the horse’s heart, central nervous system and liver. It is important for your veterinarian to recognize the condition early to ensure that fewer animals are affected.

Equine leukoencephalomalacia (ELEM), also called moldy corn poisoning, can lead to serious neurological issues and often death in horses that consume contaminated feed or corn.

For many horses, the disease comes on suddenly and few symptoms are seen prior to their death. Early signs that may be seen include:

• Disinterest in eating
• Lethargy
• Depression

Should your horse survive these initial symptoms, neurologic abnormalities connected to the sensorimotor cortex will be noticed. This includes:

• Excessive sleepiness
• Facial or pharyngeal muscle weakness
• Lack of voluntary muscle coordination
• Tendency to lean to one side
• Facial desensitization

Horses that exhibit these signs will typically be laying down and comatose within one to ten days. Prior to their death they may experience convulsions. Some horses may also experience frantic behavior, profuse sweating, delirium and/or blindness.

Types 

The toxin that causes Leukoencephalomalacia can lead to two different syndromes; neurotoxicity and hepatotoxicity.

The neurotoxic form is typically connected with the chronic consumption of low FB1s. The hepatotoxic form is usually associated with sudden exposure to a large amount of the toxin. The neurotoxic form is more likely to be seen in horses.

This illness occurs when a horse eats feed or hay that is contaminated with fumonisin mycotoxins. Three species of fusarium produce fumonisins: F. proliferatum, F. verticillioides and F. subglutinans. There are many types of fumonisins, though the two of significance in this condition are fumonisins B1 and B2. While other animals and humans can be affected by fumonisin contamination, horses are the most sensitive, experiencing signs of neurological damage after consuming only a small amount.

Your veterinarian will conduct a full physical examination of your horse and ask you for information about the symptoms you have noticed, when you first noticed them and any changes that you have seen. Your veterinarian may request a sample of the feed your horse has been eating so that he can test in for contamination. Confirming the diagnosis is only possible after the horse has died, through necropsy.

There is no treatment for leukoencephalomalacia. Should your horse develop the condition, or should you suspect that he has, you will want to remove the possibly contaminated feed from his diet. Your veterinarian will recommend that you provide him with supportive care and activated charcoal may help to decrease the absorption of the toxin. While some horses will survive the illness, when they do they will likely have cognitive and proprioceptive function deficits. 

It is important that the condition be recognized quickly. This way the contaminated feed can be taken away and no further illness to your horse or other animals will occur. Any time a feed is questionable, it should not be given to horses.

Should your horse be experiencing a severe case of the condition, your veterinarian may recommend euthanasia. Necropsy then may be conducted to confirm that the cause of his condition was feed or corn contaminated with fumonisin mycotoxins.

Should your horse survive leukoencephalomalacia, he will likely experience permanent neurological damage.

Prevention is the best treatment when it comes to this condition. Unfortunately, there is no screening test for the toxin and most corn is infected by the mold anyway. The toxin has also been found in some commercial pelleted feed, therefore it is recommended that feed be purchased only from mills that use quality corn in making their product.