Introduced from Europe, poison hemlock is now found throughout North America, growing along roadsides, ditches, cultivated fields, and waste areas especially where the ground is moist. It is a prolific seed producer and will form dense stands if left unch
Cattle, sheep, goats, pigs, horses, wildlife, birds, and man.
The two predominant toxic alkaloids are coniine (mature plant and seeds), and gamma-coniceine (young growing plant). The mechanism of action of the Conium alkaloids is complex as they appear to have a profound effect in blocking spinal cord reflexes, and an initial stimulatory followed by depressant effect on the nervous system. Large doses of alkaloid cause skeletal muscle stimulation followed by neuromuscular blockade and paralysis. The effects of coniine are similar to those of nicotine both in the central and peripheral nervous system.
In small doses, the alkaloids cause skeletal defects in the developing fetus.
The leaves and stems are the most toxic part of the plant prior to the development of the fruits. The seeds are highly toxic and can be a source of livestock poisoning when they contaminate ceral grains fed to livestock. Plants growing in the warmer southern states appear to be more toxic than those in the northern areas. Drought stress increases the alkaloid content of the plant.
The Conium alkaloids are detectable in the milk of cows and presumably in the milk of other lactating animlas grazing the plant. (Panter, E., James, F., 1990. Natural plant toxicants in milk: a review. Journal Animal Science 68, 892–904.)
Poison hemlock is a coarse, erect, 4-6 feet tall biennial or perennial plant. The smooth, branching stems are hollow, with purple spots especially near the base. The root is a simple carrot-like tap root. Leaves are alternate 3-4 times pinnately dissected, coarsely toothed with a fern-like appearance. The terminal inflorescence is a compound flat topped, loose umbel with multiple, small, white 5-petaled flowers. Fruits are grey-brown ovoid, ridged, and easily separated into two parts. The plant including the root has a strong pungent (likened to mouse urine)odor that makes it generally unpalitable.
Salivation, abdominal pain,
Muscle tremors, and incoordination
Deformities of the legs, cleft palate, abnormal curvature of the spine (scoliosis) similar to those caused by lupine poisoning will occur in pregnant cows that eat poison hemlock in the first trimester of pregnancy.
No specific treatment. Supportive therapy is indicated
Rapid, weak pulse, cyanosis of the mucous membranes,
Death from respiratory failure occurs in 2-3 hours
Respiratory paralysis, and coma without convulsions preceed death.
Abortions will occur in pregnant animals that survive the acute toxicity.
Sudden deaths with evidence of hemlock having been eaten by the animal.
All hemlock should be removed from pastures to which animals have access. Destroying the plants by mowing or with herbicides prior to the seed stage greatly reduces the chances of hemlock becoming a problem to livestock.
The plant is most toxic in the early growth phase, and cattle should not be given access to the plant during the spring when the plant is rapidly growing.