Poison Hemlock

(Conium maculatum)

Poison hemlock, which is poisonous to horses



Plant Description

Poison hemlock is a plant that grows quite large...in fact, they often grow over 6 feet tall! One of the most distinguishing features of the plant is the purple spots that can be found on the hollow stem. The plant also has white flowers, which are found in small clusters. The plant is part of the parsley family, and as a result smells like parsnip when it is damaged.

Geographic Locations

This plant can be found throughout the United States and Canada. It usually prefers to grow in moist, rich soils, so it will most often be found in woodlands and along fence rows.

Toxic Plant Components

The entire young plant, including roots and seeds are toxic. However, as the plant matures, the toxic component is stored in the seeds, leaving them the most toxic. The plants are toxic fresh or dried, so it can cause problems if baled into your hay.

Toxicity Cause and Symptoms

The onset of poisoning by this plant is extremely quick, with death often occurring in hours. Unfortunately, usually the most common sign of poisoning is finding the dead animal in the pasture.

Signs that appear shortly after consumption of the plant include:

  • Burning in the mouth
  • Salivation
  • Loose stools
  • Frequent urination and defecation
  • Muscle tremors
  • Muscle weakness
  • Impaired vision and dialated pupils
  • Disorientation
  • Extreme nervousness
  • Coma
  • Death

Cure and Treatment

Clearing the stomach of its contents is often the treatment for poison hemlock toxicity. Respiratory support may also be required, since death is the result of respiratory failure in these poisoning cases. If the stomach can be cleared sufficiently, and the horse supported until the remaining leaves pass through the digestive tract, it is possible to save the horse.


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