Animal Care

Slobbers or Slaframine Poisoning in Horses

When the weather is cool and damp, most likely in the spring or autumn, you might notice your horse drooling profusely while grazing on pasture. As long as there are no other symptoms, such as fever, this drooling is likely caused by slaframine toxicosis—or slobbers. The cause of slobbers lies hidden in your pasture grass. Horses with slobbers can produce large amounts of saliva. Slobbers are fairly harmless, with no long-term effects, but it’s important to distinguish between slobbers and a few other diseases that are more serious.


Slobbers, Slaframine Poisoning, Slaframine Toxicosis, clover toxicity.

Causes of Horse Slobbers

Slobbers or slaframine poisoning occurs when a horse eats white or red clover, alsike clover, and alfalfa growing in its pasture that is infected with a fungus called Rhizoctonia leguminicola. This fungus tends to grow during wet cool weather and appears as black spots on the plant, resulting in its common name of “black patch disease.”

WARNING: The black patch fungus produces a mycotoxin (fungus-produced toxin) that causes the horse to drool excessively.

Symptoms of Horse Slobbers

Although slobbers are usually harmless, there are other more serious symptoms that may appear in particularly sensitive horses. Some horses may show slight colic symptoms. Excessive tearing of the eyes may also occur and diarrhea is possible. There is one case of a mare aborting a foal mentioned on the OMFRA fact sheet, but this is the only reported case of reproductive issues with this relatively common toxicosis. 

It is important, however, to be sure that the drooling is not a sign of another disease. Drooling can be a symptom of Vesicular Stomatitis and can also be caused when a horse’s mouth is irritated by a chemical, or by eating irritating plant-like raspberry canes or buttercups, grains with prickly barbs, or plants with sharp burrs or leaf edges. Horses that snatch snacks while you trail ride may irritate the corners of their mouths, causing drooling and bleeding. Check your horse’s gums, tongue, lips, and palate for signs of irritation or lesions.


If you suspect vesicular stomatitis—i.e., if there is an outbreak in your area–you should call your veterinarian to confirm a diagnosis as this is a reportable disease to the state veterinarian’s office. However, if you are confident there is no other disease or plant irritation, and the horse has no fever or other clinical signs, you may suspect slobbers are the cause.


Horses will start within a few hours of eating the infected plant and will continue as long as the horse has access to the legumes with the black patch. If you remove the horse from the pasture, it should start to recover within about one to two days. 


Most horses recover quickly without treatment as long as access to the fungus-ridden plants is restricted. Mowing the pasture can help cut down infected plants, and they should grow back healthy. Since the growth of the black patch fungus depends on the weather, some years will be bad for slobbers, and others will see none. If you suspect that the fungus is in your hay, try to separate out sections that contain the legumes. Sometimes this is impossible. The toxicity of the fungus will decrease as the hay ages, so it may be a matter of waiting a few months before feeding the hay again.


There’s really very little that can be done to prevent slobbers other than preventing horses’ access to legumes during cold, wet weather. It isn’t practical to try to remove alfalfa and clovers from your pastures, as they make a valuable contribution to your horse’s nutrition and tend to be hardier in dry weather than grasses.


The divine scriptures are God’s beacons to the world. Surely God offered His trust to the heavens and the earth, and the hills, but they shrank from bearing it and were afraid of it. And man undertook it.
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