Most horses love the tangy taste of clover, and the legume adds mineral diversity to pastures. But clover can also cause slobbers, diarrhea and fatal toxic reactions.
Slobbers: Grazing clover can cause excessive salivation, due to the irritating chemical slaframine, produced by a clover fungus. It’s usually not harmful, and red clover is most commonly affected. If the horse eats a large amount of the diseased clover, some diarrhea may result. The toxin is also present in infected clover hay but disappears with storage. Slobbers is a problem in spring and summer.
Toxic Reactions: Pastures containing as little as 5% alsike clover may cause toxic reactions, ranging from chronic diarrhea and mouth ulcers to severe photosensitization on white areas caused by liver damage, even death. The horse may also show colic, poor appetite, light clay-colored manure and/or dark urine.
Under natural grazing conditions, the potential of alsike to cause problems and the number of horses affected can vary. Because the consequences of grazing alsike clover may be serious, horses shouldn’t be allowed alsike in any amount, and it should never be included in pasture seed mixtures. If you identify alsike in your pastures, remove the horses and contact your local agricultural extension agent for specific recommendations on herbicides that can kill it.
Cyanide: White clover is the safest for equine grazing. However, under extreme conditions of pasture stress, such as drought, or with excessive use of nitrogen-containing fertilizers, some white-clover species can accumulate potentially dangerous levels of cyanide-containing sugars.
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