Several species of Onchocerca ( Filariidae) occur in horses, donkeys, cattle, sheep, and goats. The adults live in nodules within the connective tissue of the host. The specific location of these nodules depends on the species of Onchocerca involved. The adults produce microfilariae which migrate through the connective tissues to the upper dermis. In cattle O. gibsoni, O. dukei, and O. ochengi produces subcutaneous and intradermal nodules in the brisket, and occasionally elsewhere. Infected animals show no other clinical signs. In horses, adult worms live in various ligaments and tendons, and the microfilariae migrate to the dermis. Cutaneous onchocercosis in horses is characterized by pruritis, alopecia, depigmentation, erythrema, and crusting. The lesions occur on the face, neck, tail head, and ventral midline. The pathogenicity of microfilariae in horses remains controversial. The lesions may be rather attributed to Culicoides hypersensivity (Summer Dermatitis or Sweet Itch) which often occurs simultaneously. Ocular lesions such as a periodic ophthalmia are reported.