Why a Horse Slobbers After Eating Clover، and What to Do

What Is Slobbers and What Causes It?
You bring your horse in from the pasture and are alarmed to see saliva pouring out of her mouth. Standing in the cross ties while you groom her، she drools a puddle on the floor.
What in the world is wrong? Does this warrant a vet call? Is this a dangerous situation or just a messy one? Why is one horse slobbering and another is not? And why is your horse slobbering this particular year after years of grazing in the same pasture?
Slobbering (Drooling) May Be Caused by a Fungus Found on Clover

What your horse is likely suffering from is "clover slobbers."
Which types of clover or plants cause horses to drool?
Red clover seems to be the most likely species 
to cause this condition، but all clovers andd

 legumes can host the fungus that causes slobbers. It is not actually the plant itself causing this problem، but a fungus that grows on the plant or hay made from red clover. The fungus Rhizoctonia leguminicola produces a mycotoxin called slaframine.
The fungus flourishes in cool، wet، and humid conditions. It appears in late spring and early summer and even in fall months as tiny black specks on the clover plants. It is so small that it is difficult to see with the naked eye.
Some horses apparently really love clover، while others can take it or leave it، which explains why some horses are affected، and others are not. Some horses may be more susceptible than others to the mycotoxins.
What else might cause a horse to slobber?