Facial eczema is a condition of severe dermatitis in cattle, sheep, and goats caused by a toxin in spores of the saprophytic fungus Pithomyces chartarum, which lives in dead vegetative material in pastures, especially perennial ryegrass. Facial eczema is an example of “secondary photosensitization,” in which the skin lesions are really the secondary result of liver damage, rather than the direct result of a plant toxin. The liver damage in facial eczema is caused by the toxin sporidesmin in the fungus spores.
Facial eczema is relatively common in areas of New Zealand and has also been observed in Australia, South Africa, and in irrigated perennial ryegrass fields in the United States (Oregon). Perennial ryegrass is the grass species most associated with facial eczema. P. chartarum as does not grow well in legumes. The occurrence of facial eczema is also influenced by livestock genetics.
Performance testing programs in New Zealand have identified genetic lines of sheep that can tolerate relatively high toxin situations. Animals suffering from facial eczema should be removed from the contaminated pasture and provided with shade, cool water, and a good diet. Feeding high levels of zinc may help prevent facial eczema.