Page 902 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Poisonous Plants of the United States Chapter | 61 857

VetBooks.ir The elimination of the toxic alkaloids in the urine is quite
rapid (t 1 /2 5 6.32 6.88 h) and begins within hours of
ingestion (Lopez-Ortiz et al., 2004). Therefore, allowing
the animal to rest and move slowly will often result in
full recovery within 24 h. There is no treatment for the
malformations, and euthanasia is recommended for the
serious skeletal defects and cleft palate. However, less
severe contracture defects, particularly of the front legs
(buck knees), will often resolve if the knee joint can be
locked within 1 week after birth. If not, the defect gener-
ally becomes worse with growth and size, and although
the animal will continue to grow, the front legs will break
down and the animal will not be adequate for the feedlot.

Summary

A reduction in incidence can be expected and has been
achieved by using one or more of the following: (1) coor-
dinating grazing periods according to plant growth stage,
(2) changing time of breeding by either advancing or
delaying or changing from spring to fall calving, (3)
reducing lupine populations through herbicide treatment, FIGURE 61.6 The hemlocks poison hemlock (Conium maculatum)
on the left and water hemlock (Cicuta douglassii) on the right. Note the
and (4) intermittent grazing between clean pastures and
tubers and partitioned stalk on water hemlock versus the single taproot
lupine pastures to break the cycle of lupine ingestion. on poison hemlock. Leaf structure is different, and poison hemlock has
purple spots on the stems.
POISON HEMLOCK (CONIUM
MACULATUM) brown with conspicuous wavy, knotted ridges. The plant
has a fleshy, usually unbranched, white taproot that looks
Poison hemlock was introduced into the United States as like parsnips. Roots have been mistaken for parsnip, seeds
an ornamental herb and grows throughout the country. for anise, and leaves for parsley.
Generally, poison hemlock grows in waste areas where The geographical distribution of poison hemlock is
adequate moisture will sustain the biennial stands. Four throughout the United States, restricted only by cultiva-
species are recognized worldwide, but only one (Conium tion and adequate moisture to sustain stands of the plant
maculatum) is found in the United States. Historically, from year to year. The plant usually grows in waste places
poison hemlock has been associated with human poison- where moisture may accumulate and protect it from
ing more than livestock and is believed to be the tea used cultivation.
to execute Socrates.
Toxicology
Description

Unlike the lupines, locoweeds, etc., multiple Conium spe-
cies are few worldwide, and only one species, C. macula-
tum, is described in the United States. Conium maculatum
is a biennial plant 1 2.5 m tall (Figure 61.6). The stems
are stout, rigid, smooth, and hollow except at the nodes. N
A distinguishing characteristic of the plant is the purple (7)
spots found up and down the main stem and a single γ-coniceine
carrot-like taproot. The leaves are large, triangular, fern- Eight piperidine alkaloids are known in poison hem-
like, and alternate on the erect stem. The stem grows the lock, five of which are commonly discussed in the litera-
second year from a rosette and taproot established from ture. Two alkaloids (coniine (5) and γ-coniceine (7)) are
seed. Frequently, seeds will germinate in the fall before prevalent and likely responsible for toxicity and teratoge-
winter and then complete their reproductive cycle the fol- nicity of the plant. γ-Coniceine is the predominant alka-
lowing year. The flowers are small, white or cream col- loid in the early vegetative stage of plant growth and is a
ored, and in umbellate clusters. The fruits are grayish bio-chemical precursor to the other Conium alkaloids