Intoxication of sheep by Astragalus arequipensis in northwestern Argentina.

Spontaneous intoxication by Astragalus arequipensis was diagnosed in a flock of 300 sheep in Jujuy province, northwestern Argentina, that grazed an area heavily invaded by this plant. The main clinical signs were intention tremors, ataxia, and progressive loss of condition. Autopsy of 2 affected animals revealed loss of body condition. The main microscopic changes were fine cytoplasmic vacuolation of cells in the cerebrum, cerebellum, thyroid and adrenal glands, kidney, liver, pancreas, urinary bladder, and lymph nodes, and swollen axons in the cerebellum. Ultrastructurally, the cytoplasmic vacuoles consisted of dilated secondary lysosomes. Composite leaf and stem samples of A. arequipensis analyzed by high-performance liquid chromatography contained 0.05% swainsonine. The diagnosis of intoxication by A. arequipensis was made based on the clinical history and signs; gross, microscopic, and ultrastructural changes; and detection of swainsonine in the plant.