Question: For the last few days, my horse has been drooling a constant flow of thin, watery saliva. What's turned on the waterworks, and should I be concerned?
Answer: On an average day, the three pairs of salivary glands in your horse's throat and under his tongue produce 10 gallons of saliva. If the output becomes a river of watery slobber, it's unsightly, but nothing to be concerned about in an otherwise healthy horse.
In most cases, excessive salivation is a response to chemical irritation. Certain oral dewormers and medications have this effect, but, in the spring and summer, clover contaminated with Rhizoctonia leguminicola fungus is the usual trigger of what is commonly called "slobbers."
Affected clover is easy to spot: The leaves change from vibrant green to a grayish tinge and eventually turn black. When consumed in moderation, forage infected by this common fungus is harmless, but its bitter taste irritates horses' salivary glands. If you find clover-induced slobbers distasteful, your only recourse is to take your horse off clover-containing pasture until the fall.
When should you be concerned about abnormal slobbering? If, in conjunction with excessive salivation, your horse has no appetite, has difficulty swallowing, is feverish and/or looks lethargic, or if the saliva is thick and unusual looking, call your veterinarian to assess the situation.
This article originally appeared in the April 1995 issue of EQUUS magazine.