Outbreaks of primary photosensitization associated with the ingestion of Froelichia humboldtiana are frequent in equidae in the Brazilian semiarid region. To reproduce experimentally the poisoning, two experimental horses were tied by a rope, in different places in a pasture of exclusively F. humboldtiana for a 16 days period. A control horse grazed in another area without F. humboldtiana. After four days both horses in the paddock with F. humboldtiana showed reddening and alopecia of the white regions of the body. After 16 days lesions were more severe with exudates and crusts. No lesions were observed in the control horse. Serum activities of γ-glutamyltransferase, aspartate aminotransferase, alkaline phosphatase, and lactate dehydrogenase were within normal values. F. humboldtiana was very palatable for the horses. These results demonstrate that F. humboldtiana causes primary photosensitization in horses after the ingestion of large amounts of plant
dermatitis; equidae; primary photosensitization; toxic plants
