What Causes the "Slobbers" In Horses?

My 2 horses have what you call the "slobbers" and I was wondering if any other legumes/grasses cause this other than red clover. I've looked up pictures of what red clover looks like and none of it looks like what I'm seeing in the pasture. What I see are very tiny trifolates growing in clumps in 2/3 of the pasture. That is where they spend most of their time and what they spend most of their time eating.

Excessive salivation in an otherwise healthy horse is actually nothing to worry about and is, in most cases, a response to chemical irritation. Some medications will have this effect and in Spring and Summer many horse owners will be familiar with the symptoms of "slobbers" (also called "Slaframine poisoning"). In most cases, this salivation is caused by a fungus called Rhizoctonia leguminicola which produces the mycotoxin slaframine. This fungus most commonly affects clover and you will notice a change from green leaves to gray or even black. The bitter taste of these leaves is what irritates horses’ mouths.

If you are sure that your pasture has no infected clover, it is possible that this case of the "slobbers" is being caused by a mechanical irritation, such as plants with tiny barbs – for example little barley, foxtail millet and hedge mustard. Only if your horse suffers from other symptoms such as lack of appetite or lethargy should excessive salivation be cause for concern.