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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

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BRIEF: What could cause these horses to drool?

I have a woman coming in at noon to look at the poisonous plants web page, but am having trouble finding the info we need. Hopefully you can narrow the search for me. She has a pasture that is very dry and weedy. The horses have used this pasture for 7 years without noticed problems, but this year they drool when they are on this pasture. She brings them in to another pasture with grass and clover, and they quit drooling. Puts them back out and they start drooling within 24 hours. The vet has checked the horses and not found anything, but hasn't checked the pasture. She just had the pasture mowed so it will be hard to ID plants, but maybe she will recognize something.


This is a common problem in drought-stricken pastures. Clovers (red and white) which harbor an endophyte fungus (Rhizoctonia) produce a alkaloid (slaframine) which causes the slobbers. This was really a hassle in the the days of draft horses in which workers started every day drenched in drool from putting on all those bridles. If the clover in the other pasture is not affected, then by all means use it. It is possible when that new pasture gets munched down low enough that the horses are eating a lot of clover, then you may see drooling there, too. I see more of this in dry years than wet, oddly enough, maybe because the grass overstory gets eaten away.