Plants that cause photosensitivity in ruminants in Brazil

This study aimed to review the mechanisms of action, clinical signs, pathology, and toxic compounds of plants that cause photosensitivity in ruminants. In addition, we sought to clarify the diagnostic methods and prophylaxis of photosensitivity-induced plants. Photosensitizing plants constitute an important group of poisonous plants in Brazil and there are at least seventeen species distributed in nine genera. Some of these plants have well known toxic compounds; in others, the substance responsible for the disease is unknown. In general, the photosensitivity can be classified as primary or secondary. Among the plants causing primary photosensitivity in Brazil, Ammi majus contains furocoumarins, while the compound in Froelichia humboldtiana remains uncertain. The known toxic compounds causing secondary photosensitivity include pyrrolizidine alkaloids, furans sesquiterpenes, triterpenes, and steroidal saponins. In other plants causing secondary photosensitization, including Stryphnodendron spp. and Enterolobium spp., the toxic compound is still unknown. Future research should be conducted in order to determine the various mechanisms of action of each toxic compound to assist the diagnosis of photosensitivity, to develop less toxic or non-toxic cultivars, or even to find new ways of preventing photosensitization.