Plants Toxic to Horses

Alsike Clover

Digger bee on Alsike clover. Photo credit: Bigstock/Dbengamin

Two disease syndromes in horses have been associated with grazing alsike clover: photosensitization and liver disease, which is less common.

• Affected species: Horses
• Low toxicity
• Common in some pastures
• Symptoms: Photosensitization (blistering of unpigmented skin when exposed to sunlight) and liver disease.
• Management: Remove horse from the pasture, manage pastures to promote grass, eliminate clover.

Photo: Photosensitivity injury

White and Red Clover

White and red clover. Photo credit: BigStock/Greywall Studio

Horses grazing pastures with red and white clover may become affected by "slobbers." The toxin behind the slobbers, slaframine, is produced by a fungus that afflicts clovers, which stimulates the salivary glands and causes horses to drool.

• The clover plant itself is not toxic.
• Slaframine is produced by "black patch fungus," Rhizoctonia, which grows on clover during periods of stress.
• Symptoms: Salivation and drooling
• Affected species: Only horses
• Management: Remove horses from clover and provide plenty of fresh water

Tall Fescue

Endophyte-Infected Tall Fescue – Kentucky 31

• Common grass in this region
• Large leaf blades with sharp edges and prominent veins, shiny on lower surface
• Not a preferred plant until after frost
• Kentucky 31 tall fescue contains an endophyte that produces a toxin called ergovaline
• The toxin is found in all plant tissues and seeds.
• Affected species: sheep, cattle, goats, horses
• Mares may have long pregnancies, abort foals, or have other reproductive problems if they graze infected fescue in the last three months of pregnancy.
• Endophyte-free tall fescue varieties are available commercially.  Novel-endophyte or "endophyte-friendly" varieties do contain an endophyte for enhanced growth but do not produce ergovaline and are safe for pregnant mares to graze.