Excessive salivation in horses can be worrisome for horse owners that have not seen it before, but “slobbers,” as the condition is often called, is usually of very little real danger. Slobbers often results from horses ingesting the compound slaframine, produced by the Rhizoctonia fungus found on legumes such as red and white clover and alfalfa.
Rhizoctonia fungus thrives on legumes during stressful times, such as high humidity, drought, and continuous grazing; therefore, slobbers is often seen in pasture situations during the summer months. Horses kept in the same pasture might experience different levels of slobbers due to their different sensitivities to slaframine and grazing preferences.
Legume hay has also been known to cause slobbers because slaframine can remain hay for several years, most commonly in red clover hay. Later cuttings of hay are most likely to contain high levels of slaframine compared to first cuttings. The Rhizoctonia fungus has a brown color visible on the live plant. Clover hay has a brown color, as well, but not due to any fungus.
For the vast majority of cases, slobbers is no more than a nuisance to horse owners. Access to fresh water will prevent dehydration and should always be provided. Other possible causes of excessive salivation can include mouth sores, foreign objects, and reactions to medication. In very rare cases, excess salivation can also be a sign of rabies, so experts do urge using an extra dose of caution around animals with excessive salivation. Check with your veterinarian to rule out any of these possibilities.
In most situations, legumes in hay or pasture