Coffee Weed or Coffee Senna
Occasionally horses, but more commonly cattle, in the southeastern United States to Texas have been poisoned by the ingestion of coffee weed (Cassia occidentalis). Affected animals develop an acute myodegeneration that can be rapidly fatal. Other species of Cassia are similarly toxic.
Coffee weeds, like other Cassia species, are erect annual legumes growing to 6.5 ft (2 m) in height, with pinnately compound leaves each with 4 to 6 pairs of leaflets. The foliage has a strong distasteful odor. The yellow flowers are produced in axillary racemes and form long linear pods that are laterally compressed to show numerous seeds. The seeds appear to contain significant quantities of the toxin. The toxin's mode of action has not been determined, although it appears to be a water-soluble protein-like compound that binds tightly to cell membranes.
Horses consuming sufficient quantities of Cassia plant are generally severely incoordinated, do not have a fever, and may die without showing other clinical signs. Unlike the disease in cattle, bloody urine rarely occurs in affected horses. Confirmation of the diagnosis is based on knowing that the animal had access to and consumed Cassia plants, along with the presence of the microscopic lesions in the muscle, kidneys, and liver.
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