Many horses will "slobber" or "salivate" when they ingest mold-infected clover. Growth of mold on clover is occasionally encountered with temperature above 80°F and humidity above 60%.

Horses with slobbers can literally fill several 5-gallon buckets full of saliva in one day. This condition is caused by slaframine, which is produced when red clover is infested with a mold. The mold is generally a rust color seen on the upperside of the leaf. This mold normally runs its course in two to four weeks, depending on weather conditions.

The slobbering is not generally a problem for the horse other than it is unsightly and may cause dehydration.

There are other weeds and fungi that occasionally cause similar problems. These may include plants the horse has consumed that have thorns, bristles, stinging hairs, or sharp awns that may cause lesions to the cheeks, tongue, and gums, causing painful ulcers and excessive salivation.