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Poison Hemlock
Poison, European, or spotted hemlock (Conium maculatum), although rarely eaten by horses or other livestock, if consumed in even small amounts, will cause sudden death. It is an erect, 3- to 6-ft (1 to 2 m) tall biennial or perennial plant. The branching stems are hollow and hairless, have purple spots especially near the base, and arise from a simple carrot-like tap root. Leaves are alternate, 3 to 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 five-petaled flowers. The fruits are grey brown, ovoid, ridged, and easily separated into two parts. Originally introduced from Europe, poison hemlock is found throughout North America growing along roadsides, ditches, cultivated fields, and waste areas, especially where the ground is moist.
At least five piperidine alkaloids, including coniine, are found in all parts of the plant, but especially in the leaves and stems prior to development of the fruits. Plants growing in the warmer southern states appear to be more toxic than those in the northern areas. Poison hemlock is toxic to all animals, including people. People are usually poisoned when they mistakenly eat hemlock for wild parsnips, parsley, or wild carrots. Livestock seldom eat the plant because of its strong pungent odor, but will do so if no other forage is available. Cattle have been fatally poisoned by eating as little as 1 lb (0.45 kg) of the green poison hemlock plant.
Signs of poisoning develop within an hour of eating poison hemlock, and if a sufficient quantity has been consumed, death from respiratory failure occurs in 2 to 3 hours. Salivation, colic, muscle tremors, and incoordination occur initially, followed by difficulty breathing, dilated pupils, weak pulse, cyanosis, coma, respiratory paralysis, and death. Abortions may occur in pregnant animals that survive acute poisoning.
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Poison hemlock may cause abnormal fetal development if it is eaten early in gestation by ewes or sows, but not mares. Affected offspring may be born with crooked legs, deformed necks and spines, and cleft palates that are indistinguishable from similar deformities caused by the teratogenic effects of Lupinus spp. and Nicotiana spp. Although pregnant mares may exhibit the acute neurologic and gastrointestinal signs of poison hemlock poisoning, the fetus appears to be unaffected.
Treatment is directed at preventing further absorption of the toxin from the gastrointestinal tract and, if possible, providing artificial respiration if respiratory paralysis is imminent.
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