Slobbers in Horses
Information taken from the Ontario Ministry of Agriculture, Food and Rural Affairs at:
Horses on pasture will sometimes start salivating profusely in a cool, wet spring or fall. Affected horses commonly show no abnormal clinical signs except the profuse frothy salivation, which is not life threatening though of concern to horse owners. This can be caused by mechanical or chemical irritation of the mouth, e.g., by plant awns; or slaframine poisoning, most commonly associated with clover pasture or hay.
Spring and fall provide cool, wet conditions that favor the proliferation of clovers in pastures. The cooler wet conditions are also ideal for the growth of the fungus Rhizoctonia leguminicola, commonly known as black patch. The fungus infects red clover (Trifolium pratense), white clover (Trifolium repens), alsike clover (Trifolium hybridum) and alfalfa (Medicago sativa). The name ‘black patch’ comes from the brown to black spots or rings observed on the plant leaves and stems. The fungus produces the mycotoxin slaframine which causes the slobbers. It can be present on both pasture and in stored dry hay. The fungus persists on infected fields from year to year. Slaframine will persist in stored hay for 10 months or more; though its biological activity decreases. Fresh hay can contain the equivalent of 50-100 ppm slaframine, which can decrease after 10 months by 10-fold to 7 ppm. Concentrations above 10 ppm may be associated with clinical signs (slobbers).
The most common clinical signs observed in horses include: excess salivation, lacrimation, colic and diarrhea. Symptoms often develop 1-3 hours after consumption of the contaminated forage and subside 48-72 hours after withdrawal from the offending forage.
In summary, clovers can be an excellent source of nutrients for horses but occasionally can become infected with fungus causing slobbers. The toxic factor (slaframine) is not life threatening and no treatment is necessary except to change the feed. Mow the pasture and regrowth (under differing environmental conditions) will likely not cause the problem.