Allium cepa & canadense
- 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.
- 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.
- 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.
- 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.
- Minimize stress and stop feeding onions. Severely anemic animals may require whole blood transfusions.
- 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.