Health & Care

Plants Poisonous to Horses

As a horse owner, you mustn’t allow certain plants to grow in your property or garden. Some of these plants poisonous to horses might be in your pasture.  It’s important to recognize them, differentiate them from your horse’s feed, and know their names and the early symptoms so that if your horse accidentally eats them, you can quickly find a solution. Here are ten common shrubs, trees, plants, and weeds that are poisonous to horses.

Tansy Ragwort

Also called groundsel, tansy ragwort weed has leaves that produce small yellow flowers. About seventy species of tansy ragwort grow along roadsides and in pastures in the United States. Various species of this plant have different toxicity levels, but they all contain some pyrrolizidine alkaloids concentration, which restrains cell division in the liver. Liver damages are irreversible and cumulative, and most horses often succumb to chronic exposure after consuming about 100 pounds.

Liver failure signs start to appear a few days after consumption: weight loss, diminished appetite and photosensitization, progressing to incoordination, jaundice, and depression. Severe stages of liver problems due to the toxin can’t be treated.

Poisonous plant for horses

Bracken Fern

Also known as eagle fern or brake fern, the bracken fern has triangular leaves that can be up to three feet high. It grows in moist open areas and woodlands. The plant contains thiaminase, which restrains thiamin (vitamin B1) absorption.

The lack of vitamin B1 causes signs similar to neural dysfunctions, including depression, blindness, and incoordination. If you discover bracken consumption before any severe neurological signs, you can administer thiamin for about a week to aid recovery.


Also called spotted hemlock or poison hemlock, this perennial weed has fernlike leaves with clusters of white flowers. There are purple spots close to the base of the stems. Hemlock grows on open uncultivated areas and along roadsides in North America. Hemlock seeds, stems, and leaves contain neurotoxins that affect a horse’s peripheral and central nervous systems.

Signs appear after one or two hours of consumption, beginning with incoordination, tremors, and nervousness, and then progressing to diminished heart rates, depression, and possibly colic. No treatment exists for this, but with supportive care, horses that consume smaller doses may recover.

Grazing Horses


Oleander shrub (also referred to as adelfa) has thick, elongated leathery leaves that grow up to ten inches long. It produces large clusters of flowers at the base of each branch. The plant contains neriin and oleandrin, which disrupt a horse’s heartbeat.

Signs may appear after several hours of ingestion. The signs include tremors, irregular heart rate, difficulty in breathing, and colic. The pulse may either accelerate or slow down. There’s a good chance of survival if a poisoned horse receives early treatment with supportive care, administering activated charcoal to prevent further toxin absorption.


Both sudangrass and Johnsongrass are coarse grasses with veined leaves that grow as high as six feet. They produce big, multi-branched seed heads. The stems and leaves of sudangrass and Johnsongrass contain a toxic compound that restrains the horse’s body from absorbing oxygen when metabolized, eventually suffocating it. Young shoots contain higher toxin concentration.

The first sign is rapid breathing, and it advances to tremors, gasping, convulsions, frequent defecation, and urinating. For less severe poisoning, you can nullify the effects by using supportive drug therapy.


Also called crazy weed, locoweed are leafy perennials with compound leaves and short stems that grow from one taproot. It produces purple or white flowers on leafless stalks. Every toxic locoweed species contains an alkaloid that prevents the growth of the enzymes needed for saccharide metabolism resulting in sugar buildup that upsets the brain cell functions.

The first sign you’ll notice in the horse is staggering, bobbing of their heads, falling, or adopting high-stepping gaits.

The effects of advanced locoism are irreversible. But less severe poisoned horses may recover after removing access to the plant.

A horse eating a poisonous grass

Red Maple Trees

Red maple trees have green leaves in summer and spring, and bright red in fall. Younger trees have smooth, pale gray barks that become broken and darker as the trees grow. Red maple leaves are more harmful when they’re wilted. Wilted leaves mostly fall from branches into pastures after storms.

Depending on the quantity of leaves consumed, signs may appear within four days after consumption. These signs include increased respiratory rate, refusal to eat, dehydration, rapid heart rate, black urine, and lethargy.

You can treat a poisoned horse by administering large quantities of intravenous fluids. Recovery depends on the quantity of leaves a horse consumed.


Yew is an evergreen shrub with flat, needlelike leaves about an inch long. It produces yellow or bright red, juicy and soft berries, with visible dark seeds. Commonly grown as ornamentals, the yew plant contains an alkaloid (taxine) that causes cardiac and respiratory collapse. Consuming a mouthful of the leaves can be harmful to horses within minutes.

The most common sign is sudden death. Horses found alive may be colicky and trembling, with a slow heart rate and difficulty in breathing. Avoidance is vital, as there’s no treatment for the consumption of the yew plant.

Water Hemlock

Water hemlock weed has hairless stems that grow up to six feet from its fleshy roots. Its stems are thick at the base with toothed and elongated leaves. Water hemlock is among the most toxic plants that grow in the United States. All its parts contain a toxic alkaloid that can affect the horse’s central nervous system.

The toxins mostly affect the brain’s neurons and cause several signs, such as convulsions, seizures, degeneration of the skeletal muscles and heart, nervousness, dilated pupils, and excessive salivation. Supportive care at the initial stage can offset the seizure effects.

Yellow Starthistle

This three feet tall spherical plant produces yellow flowers surrounded by several stiff spines. It contains a toxic compound that controls chewing and disrupts the functioning of the nerves.

A poisoned horse may have clenched or tense facial muscles and may not be able to chew or bite food effectively. The horse may also lose weight. Neural damages are permanent, and there’s no treatment.

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