Your horse is drooling. Is he thinking about dinner or could something more troubling be to blame?
To find out, first do a quick check of his face or head for signs of nerve damage. Is one ear or eyelid drooping? Does he react to a menace test by blinking when you move a finger toward his eye? Can he easily take a treat from your palm and chew it?
Next, carefully check his mouth and teeth. Can you see any foreign objects or broken teeth? Take a quick sniff of his breath: An infection that would lead to drooling will give off a bad odor.
Take a look at his nose. Is any saliva coming out of his nostrils? If so, he may have an esophageal obstruction (choke).
Finally, check your horse for signs of systemic illness. Does he have a fever? Is he lethargic or oblivious to his environment?
If your horse otherwise seems normal, he may have ingested something that caused him to drool. One common culprit is slaframine, a soaplike chemical produced by the plant fungus Rhizoctonia leguminicola, which commonly infests clover. A horse who ingests the fungus usually slobbers as he eats and when he's standing still. You're likely to notice a puddle forming at his feet as he's being groomed. This harmless condition requires no treatment. It will go away in a few weeks when the fungus growth subsides.