Slobbers or Slaframine Poisoning in Horses

Horse with slobbers.

K. Blocksdorf

Introduction to Slobbers or Slaframine Poisoning in Horses:

When the weather is cool and damp, most likely in the spring or autumn, you might bring your horse into its stall to find it drooling quite profusely. 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, and while it's not overly harmful, it is inconvenient. Horses with slobbers can drool cups of saliva at a time, leaving pools of frothy drool on the floor. The amount of saliva a horse can produce is huge. Slobbers is 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


Slobbers or Slaframine Poisoning occurs when a horse eats a white or red clover, alsike clover and alfalfa growing in its pasture or preserved in its hay. During wet cool weather, clover grows quickly, and along with it can grow a fungus called Rhizoctonia leguminicola, more commonly called black patch. Black patch appears on the leaves of the legumes as brownish or blackish irregular spots or rings that cover the leaves and stems of the plants.


The black patch fungus produces a mycotoxin (fungus produced toxin) that is irritating to the horse’s tongue, gums, and other mouth tissues and causes the horse to drool excessively.

It is possible, but carrots that have a fungus on them may cause drooling as well.  


Although slobbers are usually harmless there are other more serious symptoms which may appear. 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 a rare occurrence. 

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 an 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—particularly if there is an outbreak in your area, you should call your veterinarian to confirm a diagnosis. However, if you are confident there is no other disease or plant irritation, and the horse has no fever or severe colic symptoms you may suspect slobbers is 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 black patch. If you remove the horse from the pasture, it should start to recover within about two days. 


Your veterinarian may treat your horse with a drug to relive the salivation and diarrhea, but most horses recover quickly without treatment as long as they can not access the fungus-ridden plants. So the only real treatment is to remove the horse from the pasture. 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.


  • Hayes, M. Horace, and Peter D. Rossdale. Veterinary notes for horse owners: an illustrated manual of horse medicine and surgery. 17th ed. New York: Prentice Hall Press, 1987. Print.
  • "The Merck Veterinary Manual." The Merck Veterinary Manual. N.p., n.d. Web. 25 May 2012.
If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.