Plants Toxic to Horses

Horse owners should learn to recognize toxic plants and be aware of the symptoms they can cause.
Plants Toxic to Horses - Articles


In This Article

Alsike Clover

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

Two disease syndromes in horses have been associated with grazing Alsike clover: photo-sensitization, 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: Photo-sensitivity injury

White and Red Clover

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

The toxin, slaframine, is produced by the Rhizoctonia fungus, 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

Tall Fescue

Tall fescue meadow grass. Photo credit: BigStock/V_Nikitenko

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 favorite 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.
  • Plant contains an endophyte that produces a toxin.
  • Affected species: sheep, cattle, goats, horses.
  • Mares have long pregnancies, and may abort foals, or have weak foals if they graze infected fescue in the last three months of pregnancy

Buttercup Species

Tall Buttercup. Photo Credit: Montana Statewide Noxious Weed Awareness and Education Program, Montana State University,

  • All livestock are affected.
  • Toxicity - low.
  • Common in pastures and marshes.
  • Poisonous part - leaves and flowers.
  • Symptoms: irritated tissues in the mouth and throat. Effects the gastrointestinal system (colic, diarrhea), excessive salivation.


Common Pokeweed. Photo Credit: Joseph M. DiTomaso, University of California - Davis,

  • Effects all livestock - especially pigs.
  • Toxicity – moderate.
  • Found in rich, disturbed soils such as barnyards, moist woodlands and pastures.
  • Poisonous part - all parts, but mainly the roots.
  • Symptoms: Effects the gastrointestinal system –( colic and diarrhea) and central nervous system – (convulsions).
  • Cooked berries are sometimes used in pies.

Nightshade Species

Bittersweet Nightshade. Photo Credit:

  • All livestock are affected.
  • Toxicity - moderate.
  • Found in disturbed soils, rich pastures, and woods.
  • Poisonous part - berries and vegetation.
  • Symptoms: Effects: central nervous system- (trembling, paralysis, shock, coma) gastrointestinal system - (colic, diarrhea and impaction).


Horsenettle. Photo Credit: Ohio State Weed Lab, The Ohio State University,

  • All livestock are affected.
  • Toxicity -moderate.
  • Distribution -pastures, cultivated fields, hay fields.
  • Poisonous part -all parts, especially berries. Remains toxic in hay.
  • Symptoms: Gastrointestinal(salivation, colic, diarrhea) and central nervous system (muscle tremors, weakness, depression).

Poison Hemlock

Poison Hemlock. Photo Credit: Jan Samanek, Phytosanitary Administration,

  • All livestock are affected.
  • Toxicity - extremely toxic, 4-5 lbs. will kill a 1,000 lb. animal.
  • Distribution - disturbed or waste areas, roadsides, ditches.
  • Poisonous part - all parts are extremely toxic.
  • Symptoms: Central nervous system - block spinal cord reflexes, muscle tremors, incoordination, paralysis, frequent urination, sudden death due to respiratory failure.

Water Hemlock

Water Hemlock. Photo Credit: Elmer Verhasselt,

  • All livestock affected.
  • Toxicity - extremely toxic (a piece of root the size of a walnut will kill a cow in 15 minutes).
  • Poisonous part - all parts, especially the root.
  • Distribution - marshes, ditches, wet pastures.
  • Symptoms: Effects central nervous system, causing nervousness, breathing difficulties, muscle tremors, collapse, convulsions, death.

Jimson Weed

Jimson Weed. Photo Credit: Howard F. Schwartz, Colorado State University,

  • All animals affected, including chickens.
  • Toxicity – extreme, one mouthful can kill a horse.
  • Distribution - crop fields, waste areas, barnyards.
  • Poisonous part - entire plant.
  • Annual plants, mowing helps eliminate plants.
  • Symptoms: Effects central nervous system. Has hallucinogenic properties

White Snake Root

White Snakeroot. Photo Credit: John Triana, Regional Water Authority,

  • Affects horses, cows, sheep, goats, pigs and chickens.
  • Toxicity – high.
  • Distribution: common in moist areas, edge of woods, along roads.
  • Poisonous part(s): leaves and stems.
  • Symptoms: trembling, stiffness, ataxia, coma, death.
  • Toxin, trematol, passes to humans in milk resulting in milk sickness.


Common Milkweed. Photo Credit: Richard Gardner,

  • Affects livestock and poultry.
  • Toxicity – high.
  • Distribution - swamps, bogs, dry fields and pastures.
  • Poisonous part - entire plant.
  • Symptoms: weakness, seizures, respiratory difficulties, coma, death.
  • Latex-like sap makes plant very unpalatable.

Cherry (Black, Pin, Choke)

Black Cherry. Photo Credit: Richard Webb,

  • Affects all livestock.
  • Toxicity - highly toxic.
  • Poisonous part – leaves, twigs, bark and seeds contain cyanide, wilted leaves are more toxic than the rest.
  • Symptoms: anxiety, breathing problems (suffocation), staggering, convulsions, collapse, death.

Red Maple

Red Maple. Photo Credit: Paul Wray, Iowa State University,

  • Only horses and ponies are reported to be affected.
  • Toxicity - EXTREMELY toxic.
  • Poisonous part - very high in wilted or dried leaves.
  • Toxins (gallic acid and others) destroy red blood cells. Silver and sugar maple also have toxins.
  • Symptoms: breathing difficulties, jaundice, dark brown urine,death.

Box Elder Maple

Box Elder. Photo Credit: Melissa McMasters

  • Causes Seasonal Pasture Myopathy
  • Seeds contain toxin, hypoglycen A, which interferes with fat metabolism and breaks down respiratory and muscle cells
  • Symptoms: Tremors, weakness, stiffness, dark urine, rapid breathing, and death – usually within 48 hours

Black Walnut

Black Walnut. Photo Credit: Jason Sharman, Vitalitree,

  • Toxicity - moderately toxic.
  • Poisonous part(s): bark, root, nuts contain juglone, which may be involved in toxicity.
  • Symptoms: horses bedded on shavings or sawdust containing black walnut develop colic, edema and laminitis.
  • No amount of black walnut is acceptable in bedding.

Oaks (Black, Chestnut, Red, Pin, White)

Red Oak Leaves. Photo Credit:

  • Affects cattle, sheep, horses and pigs.
  • Toxicity - moderately toxic.
  • Poisonous part - New young leaves most toxic, acorns more toxic when green than when mature.
  • Symptoms: Poor appetite, weight loss, diarrhea, increased drinking, increased urination, kidney failure, edema, death.

Buckeye or Horse Chestnut

Horse Chestnut. Photo Credit: John Ruter, University of Georgia,

  • Affects all livestock.
  • Toxicity - moderate to high toxicity.
  • Poisonous part - leaves, seeds, young sprouts; poisoning in spring due to early sprouting.
  • Symptoms: Gastrointestinal and central nervous systems.

Black Locust

Black Locust. Photo Credit: Jan Samanek, Phytosanitary Administration,

  • Affects all livestock species
  • Toxicity – moderate to high
  • Poisonous parts - leaves, seeds, bark, wood (fence posts)
  • Symptoms – Causes severe gastritis, colic, depression

Rhododendron, Mountain Laurel, Azalea

Rhododendron. Photo Credit: Richard Webb,

Common landscape shrub, also found in the forest.

  • Affects all livestock.
  • Toxicity - moderate.
  • Poisonous part - all parts.
  • Symptoms: Stomach irritation, abdominal pain, abnormal heart rate and rhythm, convulsions, coma, death.

Bracken Fern

Bracken Fern. Photo Credit: David Stephens,

  • All livestock are affected.
  • Toxicity - low to moderate.
  • Distribution - moist forests.
  • All plant parts contain toxin, toxin destroys Vitamin B1.
  • Symptoms: Weight loss, weakness, gait abnormalities, abnormal heart rate and/or rhythm, inability to rise, death.

Yew (English or Japanese)

Yew. Photo Credit: Richard Webb,

  • Toxicity - EXTREMELY toxic.
  • Poisonous part - all plant parts, especially high in leaves during winter.
  • Symptoms: Muscle trembling, incoordination, colic, slow heart rate, death.