Slaframine Toxicosis in Horses

Slaframine is a mycotoxin that is produced by the fungus Rhizoctonia leguminicola. When a horse eats red clover, or other forage or hay that has been infected by the fungus, the slaframine causes the horse to drool by stimulating the salivary glands. This excessive salivation, also called Slobbers, is the main symptom of slaframine poisoning, and is a mild condition that can be cleared once the offending feed is removed.

While red clover is the most common plant infected with the Rhizoctonia leguminicola fungus, other plants can become infected too, including white clover, alsike, alfalfa, and soybean. The fungus thrives on these legumes in stressful conditions, such as wet weather, high humidity, drought, and continuous grazing. The characteristic black or brown circular areas it creates on the leaves of contaminated plants is seen mostly during summer months, and is called black patch disease. The fungus can survive winters, and can live several years on hay and seeds. Because of the heartiness of the Rhizoctonia leguminicola fungus, proper forage and feed management is needed to prevent your horse from ingesting the slaframine toxin.

Symptoms of slaframine poisoning are apparent within hours after a horse first consumes contaminated clover or hay, and can last up to three days. While symptoms are generally mild and do not affect the health of the horse in any dramatic way, severe cases of the salivations descending into the lungs can cause death by suffocation. Horses grazing in the same infected pasture may exhibit varying levels of symptoms due to differences in sensitivities to the toxin and grazing patterns. Symptoms include:

• Slobbers, or excessive salivation
• Diarrhea
• Feed refusal
• Mild bloat
• Shedding tears
• Stiff joints
• Increased and frequent urination
• Anorexia
• Weight loss
• Skin lesions
• Excess salivation in lungs
• Difficulty breathing
• Emphysema
• Suffocation

The main cause of slaframine toxicosis is the ingestion the Rhizoctonia leguminicola fungus that has infected food sources, such as red clover or hay. The fungus produces the mycotoxin slaframine which stimulates the salivary glands and pancreas to create excessive salivation and other related symptoms.

Diagnosis of slaframine toxicosis is based on the symptoms and the presence of the Rhizoctonia leguminicola fungus on your horse’s food source. This could be seen as black patch disease on pasture forages, such as clover or alfalfa. The fungus can be detected visually on the leaves, or through cultures or chromatographic methods on the hay or silage. Chromatography can also be used with the plasma or milk of the affected horse.

Symptoms of this condition are similar to other disorders, such as rabies and mouth disorders, and your veterinarian may perform further testing to rule those causes out.

Treatment for slaframine toxicosis is as simple as the removal of the suspected feed or forage from your horse’s diet, which results in a full recovery within 24 to 48 hours. The disease is short term and may need no further treatment.

In some cases, atropine can be used to reduce salivation and other signs associated with the gastrointestinal system. Fresh water should always be readily available to prevent dehydration.

While excessive salivation can seem to be a nuisance, it isn’t a major health concern for your horse. Identifying and removing the contaminated food is needed for the recovery of your horse, which results in a complete cessation of symptoms and a returned appetite within 24 to 48 hours. In very rare cases where the salivation descends into the lungs, death can occur by suffocation.

Through forage and feed management, you can prevent your horse, or others in the population, from acquiring this condition. Ways to do this can include:

• Planting clover varieties that are more resistant to black patch disease
• Reducing the use of red clover, or diluting it with other foodstuffs
• Removing red clover with broad leaf herbicides for pasture use
• Grazing or harvesting red clover during late bud to early bloom
• Storing second cutting hay made from red clover until the next year to help decrease the amount of slaframine
• Mowing pastures with black patch disease down until the spots are no longer present
• Replacing contaminated forage and feed
• Over-seeding pastures to increase the concentration of grasses
• Applying nitrogen fertilizer during spring and fall seasons
• Rotating and resting pastures to give the grass time to grow taller than the clover