10 Most Poisonous Plants for Horses


In the United States there are hundreds of dangerous plants for horses. Sometimes it can be hard to keep up to date on them all. We have compiled a list of the 10 most poisonous ones to help you keep your horse safe.



Dangers: All parts of this plant (except the berries) contain a toxin that causes  respiratory and cardiac collapse. This can kill a horse within minutes of consuming a mouthful. The leaves will stay toxin even when they have dried up. Symptoms: Colicy horses is the main symptom if the horse is found alive. The most common sign is immediate death.

Is there a treatment?: There is currently no cure or treatment for this toxic plant.




Dangers: This plant contains a toxin that has an effect on the brain. This inhibits the nerves and chewing. Horses must consume 50 to 200 percent of their body weight over a months time to be in danger.

Symptoms: Clenched jaw, unable to chew, and weightloss.

Is there a treatment?: There is no treatment. Euthanasia is recomended.

Where can this be found?: All throughout the western United States.

Water Hemlock

waterhemlock.jpgDangers: This is one of the most toxic plants found in the United States. The stem and roots are the most poisonous part of the plant. It will only take less than a pound of this plant to be fatal. These toxins affect the central nervous system. Signs appear about an hour after the plant is consumed and death will follow and hour later. Most animals will avoid this plant.

Symptoms: Convulsions, rapid breathing, muscle damage. 

Is there a treatment?: Supportive care will help, any horses that survive will have skeletal muscle damage and heart problems for life.

Where can this be found?: Found throughout the entire United States. Usually seen in marshy areas and meadows.



Dangers: This plant contains a toxin that inhibits cell division in the liver. Damage to the liver is irreversible. Most horses will succumb to chronic liver failure after comsuming about 50 to 150 lbs.

Symptoms: The levels of toxins varies from species to species. There are often no signs until liver failure. Then you will see weight loss, depression and juandice.

Is there a treatment?: There is no treatment for advance liver failure.

Where can this be found?: Throughout the entire United States. This is often seen in pastures and along the side of the road.

Red Maple Tree

redmapletree.jpgDangers: The fresh maple leaves do little to no harm at all. Although, the wilted maple leaves can be extremely fatal if comsumed. These toxins cause the red blood cells to break down, causing the blood to carry little oxygen. As little as a pound of leaves can be fatal.

Symptoms: Signs can appear within hours or take up to 4-5 days. Horses will be lethargic, with red or dark brown urine and they will often refuse to eat. 

Is there a treatment?: Blood transfusions and IV fluids will often help.

Where are these found?: These are most often found in the eastern part of the United States.



Dangers: All parts of this plant contain a toxin that will disrupt the beating of the heart. 30 to 40 leaves will kill a horse and the leaves remain toxic after they wilt.

Symptoms: Signs appear hours after ingestions and will normally last about 24 hours. Signs will include trouble breathing, colic, tremors and irregular heart beat.

Is there a treatment?: Supportive care and activated charcoal will often stop more toxins from being absorbed.

Where are these found?: Will only grow in hot climates, but is often planted in pots in the northern areas of the United States,

Loco Weed


Dangers: This toxin disrupts the function of brain cells.

Symptoms: Strange behavior. This includes high steps, bobbing of the head, staggering and falling.

Is there a treatment?: There is no treatment and the effects are irreversible. Horses with less severe signs may recover once the weed is removed from the pasture.

Where are these found?: Can be found in the West and South West area of the United States. Often in dry sandy areas.

Johnsons Grass

johnsongrass-3d54.jpg Dangers: This grass contains a Cyanide compound which inhibits the body's absorbing of oxygen.

Symptoms: Signs are very similar to cyanide poisoning. These include rapid breathing, tremors, frequent urination, gasping and comvulsions.

Is there a treatment?: Supportive drug therapy can sometimes offset the toxins.

Where are these found?: This grass is native to southern areas of the United States.


johnsongrass-3d54.jpg Dangers: This plant contains toxins that will affect the horses central nervous system. 4-5 pounds would be a fatal amount to consume.

Symptoms: Signs will include nervousness, tremors, staggering and depression. This will all lead up to death from respiratory failure.

Is there a treatment?: There is no treatment. If a horse consumes a smaller amount, supportive care will often work.

Where are these found?: This grass grows wild around the entire United States.

Bracken Fern

johnsongrass-3d54.jpg Dangers: Consumption of this plant will eventually lead to neurological impairment. This plant is unique in that some horses will develop a taste for it and will actually seek it out in the pastures.

Symptoms: Signs will include depression, blindness and incoordination.

Is there a treatment?:Giving the horses thiamin will often reverse the effects if the signs or not severe.

Where are these found?: This can be found coast to coast in the United States.