Castor Oil Plant
Castor oil plants (Ricinus communis) are common perennial plants of tropical areas, growing 6 to 13 ft (2 to 4 m) high, with a single, hollow branching stem. The stem is often purplish in color with a waxy coating. Leaves are large, alternate, usually 8 lobed, each with a main vein that radiates from the off-centered attachment of the petiole. Yellowish flowers are produced in racemes at the end of the main stem and form fruits covered with soft spines that dry into sharp spines surrounding three characteristic seeds. Poisoning occurs from eating either the plants or grain contaminated with castor beans.
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All parts of the plant and especially the seeds contain ricin, a highly toxic lectin that inhibits protein synthesis. Similar toxic lectins are found in rosary peas (Abrus precatorius) and black locust (Robinia pseudoacacia). Lectins are proteins that have the capability of binding to cells; they can cause agglutination of cells and acute hypersensitivity reactions. Horses are poisoned by eating seeds (castor beans) in an amount as small as that equal to 0.01% of their body weight. This amount could be provided by only 1 to 2% castor beans in the horse's grain. However, castor oil extracted from the seeds is not toxic, as the ricin is insoluble in the oil. The oil is, however, a potent intestinal purgative or cathartic.
Early signs of castor bean poisoning in horses include trembling, sweating, and incoordination which appear several days after the animal has eaten grain contaminated with castor beans. Colic, diarrhea, and a rapid weak pulse develop as the poisoning progresses. Horses that develop clinical signs seldom survive.
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