Plants Toxic to Horses

Alsike Clover

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.

White and Red Clover

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.

Buttercup Species

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

Pokeweed

• Affects 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 - Affects the gastrointestinal system (colic and diarrhea) and central nervous system (convulsions).
• Cooked berries are sometimes used in pies.

Nightshade Species

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

Horsenettle

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

Poison Hemlock

• All livestock are affected.
• Toxicity - extremely toxic, 4-5 pounds will kill a 1,000 pound animal
• Distribution - disturbed or waste areas, roadsides, ditches
• Poisonous part - all parts are extremely toxic
• Symptoms - Affects the central nervous system (blocked spinal cord reflexes, muscle tremors, incoordination, paralysis), frequent urination, sudden death due to respiratory failure.

Water Hemlock

• All livestock are 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 - Affects central nervous system, causing nervousness, breathing difficulties, muscle tremors, collapse, convulsions, death.

Jimson Weed

• All animals affected, including chickens.
• Toxicity – extreme
• Distribution - crop fields, waste areas, barnyards
• Poisonous part - entire plant, especially seeds
• Symptoms - Affects central nervous system. Has hallucinogenic properties
• Jimson weed has a strong, foul odor and an unpleasant taste. Animals are often poisoned when feed is contaminated with jimson weed seed.
• Jimson weed is an annual plant; mowing helps eliminate these plants.

White Snake Root

• Affects horses, cows, sheep, goats, pigs and chickens.
• Toxicity - high
• Distribution - common in moist areas, edge of woods, along roads
• Poisonous parts - leaves and stems
• Symptoms - trembling, stiffness, ataxia, coma, death
• White snake root's toxin, trematol, passes to humans in milk resulting in milk sickness.

Milkweed

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

Cherry (Black, Pin, Choke)

• Affects all livestock, most dangerous to ruminants.
• 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

• Only horses and ponies are reported to be affected.
• Toxicity - extremely toxic (1.5-3 pounds cause toxicity)
• Poisonous part - wilted or dried leaves
• Symptoms - breathing difficulties, jaundice, dark brown urine, death.
• Toxins (gallic acid and others) destroy red blood cells. Red maple hybrids, such as silver and sugar maple, also have toxins.
• Leaves are most dangerous when wilting (i.e. a branch comes down during a storm), but fallen autumn leaves are also toxic for 30 days or so and should be removed from pastures.

Box Elder Maple

Seeds from the boxelder maple cause the equine muscle disease Seasonal Pasture Myopathy.

• Affected species - horses
• Toxicity - high. Quantity required for toxicity is unknown, but SPM is 75-90% fatal.
• Poisonous parts - Seeds contain toxin, hypoglycen A, which interferes with fat metabolism and breaks down respiratory and muscle cells. Only female boxelder trees produce seeds. Male trees are not dangerous.
• Symptoms - Tremors, weakness, stiffness, dark urine, rapid breathing, and death – usually within 48 hours

Black Walnut

• Species affected - horses
• Toxicity - moderately toxic
• Poisonous parts - bark, root, nuts contain juglone, which may be involved in toxicity. Walnuts and hulls on the ground may become moldy and cause toxicity if consumed.
• Symptoms - Horses bedded on shavings or sawdust containing black walnut develop colic, edema and laminitis.
• No amount of black walnut is acceptable in bedding.
• If removing trees or branches in pastures, be careful to clean up all sawdust left in the pasture.

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

• 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

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

Black Locust

• 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

Common landscape shrub, also found in the forest.

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

Bracken Fern

• All livestock are affected.
• Toxicity - low to moderate
• Distribution - moist forests
• Poisonous part - All plant parts contain toxin which destroys vitamin B1.
• Symptoms - Weight loss, weakness, gait abnormalities, abnormal heart rate and/or rhythm, inability to rise, death
• Some animals develop a preference for this plant.

Yew (English or Japanese)

• Affects all livestock and humans
• Toxicity - Extreme
• Poisonous part - all plant parts, especially high in leaves during winter.
• Symptoms - Muscle trembling, incoordination, colic, slow heart rate, death.
• Yews are commonly planted as landscape shrubs on home properties and even show grounds.