A scary sight for a horse owner is to walk into the stall and see large amounts of saliva pouring from the horse’s mouth.  There are certainly several causes for this, such as choking or a blocked esophagus, exposure to certain insecticides, inability to swallow, or inflammation of the oral cavity. However, maybe the most common cause of excessive salivation is a condition appropriately called slobbers.  Slobbers occurs when a horse ingests pasture, hay, or silage that contains a fungus that is commonly found in soil and transmitted in seeds.  The fungus produces a mycotoxin called slaframine that produces the clinical signs of excessive salivation.  Other clinical signs include diarrhea, excessive tearing, frequent urination, stiffness, abortion, loss of appetite, bloating, and even death.  However, most cases simply have excessive salivary production that stops 24 hours after removing the infected hay. 

The fungus can be seen growing on the plants. Dr. R.H. Poppenga from U.C. Davis indicates the infection begins as a black to bronze patch on the leaves, usually on their underside.  The fungus will eventually spread and cover the entire plant, killing the plant.  Symptoms in animals eating the plants will depend on the concentration of the fungus.  The fungus is most commonly noted on red clover but can be found on many other plants including white clover, soybean, blue lupine, cow pea, alsike clover, and alfalfa.  If your horse is salivating excessively, it could just be due to fungus in the hay.  However, there also could be other problems such as botulism, so a vet exam is recommended.