Poison hemlock (
Conium maculatum) is an annual or biennial herb of the Apiaceae family. It is native to Europe and western Asia and was introduced into North America in the 1800s as an ornamental but has since then, escaped cultivation and now widely distributed across much of the United States and adjacent areas in Canada. As a biennial, poison hemlock produces leaves as a basal rosette it's first year of growth, which develops into an upright flower stalk during the second year.
Poison Hemlock Toxic Components
Poison hemlock contains eight piperidine alkaloids, however y-coniceine and coniine are generally the most abundant and the predominant cause of acute and chronic toxicity in horses. Coniine is a pyridine derivative similar in structure and function to nicotine. These toxins have a direct effect on the horse's nervous system, neuromuscular junction, and brain. Poison hemlock toxicity varies depending on the stage of growth, environmental conditions (rain, temperature, cloud cover), and soil. Toxicity increases throughout the growing season, especially in the roots, which resemble parsnips. Although all parts of the plant are toxic, the most toxic parts are the fruits when they are still green, and stems.
Signs of Poison Hemlock Poisoning in Horses
Signs of
poison hemlock poisoning in horses develops 1 to 2 hours after ingestion. Horses don't typically graze hemlock unless food is scarce, or it is contaminated in hay. The lethal dose of poison hemlock ranges from 0.2 to 0.8% body weight or 2 to 8 lbs per 1,000-pound horse.
What Poison Hemlock Looks Like
- Height: 2 to 3 m (6.6 to 10 ft) tall
- Stem: Hollow, erect, branched, upright flower stalk the second year of growth. Light green, hairless, with distinctive purplish spots or blotches.
- Leaves: Delicate, parsley or fern-like, large and lacy, alternate and basal, with the upper leaves progressively smaller. Leaflets are glossy green (that are darker on the top side), minute, lance-shaped, and have serrated edges. Leaves are attached to stems by leaf stalks (petioles).
- Flowers: Small, white, 5-petaled, in terminal, umbrella-shaped clusters that are between 1 to 3 inches in diameter.
- Root System: Long white taproot with fibrous secondary roots.
