Usually found in moist meadows and thickets but some species may occur on open hillsides and in sandy bottom lands
Cattle and cats are the most susceptible to onion poisoning, horses and dogs are intermediate, with sheep and goats being the most resistant. Dog breeds such as Akitas and Shibas are especially sensitive to onion poisoning.
An alkaloid, N-propyl disulphide, present in both cultivated and wild onions, chives, and garlic causing oxidative injury to the hemoglobin and red blood cell membrane. The hemoglobin, once damaged, precipitates into Heinz bodies visible in the red blood cells. Diets containing more that 25% dry matter of onion will cause clinical anemia.
Herbaceous plants with bulbs and narrowly linear leaves. The leaves are sheathing, usually basal and hollow. The stem is simple and erect with a terminal umbel subtended by 2 or 3 membranous bracts. The flower may be white, purple, pink or green and have a six-parted perianth. The flowers are borne on slender pedicels. All parts of the plant smell of onion if crushed.
Allium candense - wild onion
There is frequently a distinct odor of onion on the breath, feces, urine and milk of poisoned animals.
Weakness and recumbency due to severe anemia.
Animals should not be stressed, and onion feeding should be discontinued until recovery from the anemia is complete. Whole blood transfusions may be necessary in severely anemic animals.
Affected animals have pale mucous membranes, a fast, weak pulse and may stagger and collapse as a result of anemia. In severely anemic animals, stress and heavy parasite infestations may be sufficient to cause death.
Increased respiratory rate.
The presence of dark red-brown colored urine (hemoglobinuria) is often the presenting sign of poisoning.
Heinz body anemia is highly suggestive.
Feeding greater than 25% onions to cattle will induce anemia and affect weight gains. Pregnant ewes can eat a diet containing up to 100% onions, and although they develop anemia, they appear able to adapt to the onions, and do not develop a fatal anemia as do cattle. Pregnant ewes eating an exclusive onion diet have a normal lambing percentage.
Feeder lambs fed onions cull onions do not gain weight if more than 50% of the diet consists of onion. Meat quality and flavor are not affected in sheep even if they are fed onions up to the day of slaughter.