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| Description. Herbaceous
plants with narrow, linear leaves. Plants have a simple, erect
stem with a terminal umbel. Flowers are white, pink, purple, or
green. When crushed, all parts of the plant smell of onion. |
| Geographic range.
Found throughout North America in meadows and
sandy bottomlands. |
| Toxic principle.
The alkaloid N-propyl disulphide is present in
cultivated and wild onions. |
| Toxicity. Cattle
are most susceptible to onion poisoning. Horses, cats, and
dogs are less susceptible. Goats and sheep are fairly resistant to
poisoning. Diets containing greater than 25% dry matter of onion
can cause clinical signs of anemia. Most poisoning is due to
cultivated, not wild, onions. In cats, a dose of 5 g/kg body weight can
cause clinical signs. |
| Mechanism of toxicologic
damage. N-propyl disulphide affects the
enzyme glucose-6-phosphate dehydrogenase in RBCs and interferes with the
hexose monophosphate pathway. This leads to insufficient phosphate
dehydrogenase or glutathione to protect RBCs from oxidative
damage. Oxidation of hemoglobin occurs and Heinz bodies are formed
by precipitation of oxidized Hb in RBCs. Anemia is proportional to
the number of Heinz bodies formed and the ability of the spleen to
remove the damaged RBCs. |
| Diagnosis
Clinical
signs. Hemoglobinuria, dark red-brown
urine, is often the first clinical sign observed. Pale mucous
membranes and fast, weak pulses are seen.
Laboratory
Diagnosis. Consistent with hemolysis.
Hematocrit may be as low as 10-15%. The regenerative response is
seen within several days. Decreased blood urea nitrogen is also
seen.
Lesions.
Grossly, a strong odor of onions will emanate from
the body and plant material may be found in the ingesta. Tissues
will have a yellowish discoloration. The liver will be pale to
golden-brown and mottled. The affected kidney is brown to mottled
black. Microscopically, hemosiderin will be seen in the kupffer
cells of the liver, macrophages of the spleen, and in renal tubular
cells. Hepatic necrosis and renal tubular necrosis may also
be seen. |
| Treatment. Minimize
stress and stop feeding onions. Severely anemic animals may
require whole blood transfusions. |
| Prevention. Balanced
food rations containing up to 25% dry matter of onion are safe when fed
to cattle. Onions should be well-chopped and mixed in cattle
rations. Do not feed baby food containing onion powder to cats. |
