Page 929 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

882 SECTION | XIV Poisonous Plants

VetBooks.ir Treatment and Control hemorrhagic diarrhea. The Nicotiana spp. contain neuro-
logical toxins including the pyridine and piperidine alka-
There are two syndromes of milkweed poisoning a neu-
loids that are responsible for toxicoses and teratogenesis.
rological one and a cardiac one. Treatment for the cardio-
Some species of Solanum cause a neurological disease in
toxic signs is approached similar to that of digitalis
cattle, sheep, and goats characterized by loss of equilib-
glycoside toxicity that is, activated charcoal, atropine
rium, tremors, ataxia, collapse, opisthotonus, seizures, and
for atrioventricular block, and/or antiarrhythmic drugs.
death. Solanum malacoxylon and Cestrum spp. contain
There is no specific treatment for the neurological syn-
vitamin D-like compounds that cause abnormal calcium
drome except symptomatic treatment to control seizures
absorption and metabolism resulting in calcified tissues,
and supportive therapy. A field test with a detection
lameness, and weight loss. Green potatoes, sprouts, and
threshold of 0.057% is available for detecting cardeno-
vines contain steroidal glycoalkaloids that are both toxic
lides in the latex of milkweeds (Sady and Seiber, 1991).
and teratogenic. Table 61.13 provides a limited overview
Knowledge of the milkweed species in the pasture, stage
of selected species, their distributions, and their toxins
of plant growth when consumed, and history of grazing
(Burrows and Tyrl, 2001; Knight and Walter, 2001).
and clinical effects are all important in developing a diag-
nosis and eliminating other causes.
In most cases, knowledge that the plant exists in one’s
pasture and prevention of ingestion is the best way to Clinical Signs
avoid poisoning. Purchase of weed-free hay to avoid poi-
The toxins in the Solanaceae family contribute to various
soning via contamination is also important. Know where
clinical effects depending on the amount of plant/toxin
the hay comes from, and always be alert as to the content
ingested, the plant species eaten, and the animal species
of the hay. Control of milkweeds can be accomplished
consuming the plant. Signs range from mild digestive
with herbicides such as 2,4-D, picloram, amitrole, or
upset to severe colic in horses when contaminated hay is
gyphosate, depending on the other forage it has infested
fed; neurological dysfunction, seizures, and death in sheep
and the circumstances. Always follow the manufacturer’s
and cattle; big head and calcification of the blood vessels;
recommendations.
and teratogenesis.
NIGHTSHADES
Treatment
The nightshade family comprises more than 80 90 gen-
era and more than 2300 species worldwide. Some of the Animals showing severe neurological signs, such as tre-
more common poisonous genera are Brugmansia, mors, ataxia, and dilated pupils, may be treated with phy-
Brunfelsia, Capsicum, Cestrum, Datura, Hyoscyamus, sostigmine. Oral activated charcoal as an adsorbent may
Lycium, Lycopersicon (tomato), Nicotiana (tobacco), be effective if administered in a timely manner. However,
Solandra, Solanum, Nicandra, and Physalis. Some com- most animals will recover if treated symptomatically and
mon nightshade species are listed in Table 61.13. In the if the animals are not overly stressed.
United States and Canada, the nightshades can be annual,
perennial, or shrubs with alternate, simple or compound
leaves, axillary inflorescences, radially symmetrical flow- KNAPWEEDS (CENTAUREA SPP.)
ers composed of five free sepals, five free petals, and usu-
ally five stamens with anthers grouped conically about The knapweeds are a large group with primarily noxious,
the stigma and berry-like fruits of variable colors. invasive characteristics. Although this genus is not a great
risk for livestock producers, a serious disease of horses
called nigropallidal encephalomalacia warrants its inclu-
Toxins
sion in this chapter. There are 450 500 species of
The nightshades have a variety of toxins known to affect Centaurea, and 29 species have been described in North
people and animals, including the tropane alkaloids, America (Burrows and Tyrl, 2001). Most of these have
which affect the autonomic nervous system by blocking been introduced and have had a huge negative impact on
the action of cholinesterase (Knight and Walter, 2001). rangelands in the western United States. Although most
This results in accumulation of acetylcholine and subse- species are opportunists and will aggressively invade ran-
quent inhibition of the parasympathetic nervous system, gelands, especially those that have been over-grazed,
causing dry mouth, decreased intestinal motility, dilated burned, or disturbed, only 2 species are of any toxicologic
pupils, and tachycardia. The tropane alkaloids also affect significance Centaurea repens (Russian knapweed) and
the GI tract, causing colic in horses, constipation, and/or C. solstitialis (yellow star thistle).