Horse Side Vet Guide ®

Equine Health Resource

Clover Toxicity

Synonyms: Slaframine Toxicity, Red Clover Toxicity, Alsike Clover Toxicity, Black Patch Disease, Slobbers

Slaframine Toxicity (a/k/a Clover Toxicity) results from ingestion of a toxin produced by the fungus Rhizoctonia leguminicola, commonly found on Red Clover (less commonly found on White Clover, Alfalfa and Alsike) that causes excessive slobbering (salivation) in horses.

This condition is fairly common in hot, humid climates and during hot, humid weather periods. It rarely is found in drier conditions.

Ingestion of small quantities of this fungus may lead to drooling, whereas ingestion of large quantities can result in more severe problems such as diarrhea, colic, frequent urination, inadequate milk production in mares, and even abortion.

This diagnosis is based on the the observation of salivation – the classic clinical sign of this toxicity – coupled with a history of grazing affected clover. Black or gray splotches of this fungus may be visible on the leaves or dark rings on the stems of the growing clover plants. It is harder to see in dried hay.

Other than removing horses from pasture or affected hay, there is no other reported treatment at this time.

Prognosis & Relevant Factors

The prognosis depends on the amount ingested. Generally, the prognosis is good if the problem is caught early, and the horse is immediately moved from the pasture and switched to an uninfected, good quality hay. Usually the signs disappear after 1-3 days. Rarely, in severe cases, however, photosensitization and/or liver disease may result.

Once plants are cut and baled, the levels of toxin decrease in hay over a period of months.


  • Are there any long-term consequences to this condition?
  • Should I avoid planting clover in my pastures altogether?
  • What happens to the toxin if the pasture is made into hay?

    Inspect your pastures and avoid grazing pastures infested with this fungus.

    If your horse is grazing pasture that may be infested, be on the lookout for signs of this disease and remove the horse immediately if there are any signs.

    When planting, mix clover with other grasses. Re-seed with clover varieties that are resistant to infection with the fungus.

    Author: Doug Thal DVM Dipl. ABVP


    Lavoie JP, Hinchcliff KW eds. Blackwell's 5 Minute Vet Consult: Equine. 2nd Ed. Ames: Wiley Blackwell 2008.


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