ABSTRACT
Photosensitization in livestock has been a problem of economic importance in various parts of the world. For example, the Arabs in Tunis painted their horses with henna or tobacco juice as a protection against hypericism and Chillo reported in 1787 that black sheep were used on the Tarantine fields because of the susceptibility of white animals to poisoning by Hypericum crispum. Photosensitization disorders are seen in a wide range of grazing farm animals as well as other animals that are kept outdoors. N. T. Clare divided the photosensitizing disorders into three main categories of photosensitization: Type I primary photosensitization; Type II photosensitization due to aberrant pigment synthesis, and Type III hepatogenous photosensitization. The chapter describes the major diseases caused by either Type I photosensitization or Type III photosensitization. Many hepatogenous photosensitization disorders are associated with ingestion of plants containing steroidal saponins.
