Geeldikkop, known as hepatic photosensitivity disease, occurs in sheep and goats. This disease is caused by feeding of Tribulus terrestris. Clinically, affected animals have dermatitis due to photosensitivity, emaciation and yellowish mucous membranes. The lesions are characterized by crystalloid materials in bile ducts, hepatic fibroplasia, bile duct hyperplasia, nephrosis and necrosis of cardiac muscle associated with infiltration of inflammatory cells. Experimental disease caused by feeding of Tribulus terrestris have showm different results. Therefore, an exprimental trial was undertaken to evaluate feeding of Tribulus terrestris in sheep in Khorasan province. 11 sheep were devided to two group: Treatment group (6 sheep) and Control group (5 sheep). During 45 days, sheep of control were given fundamental diet and sheep of treatment were given fundamental diet (20%) and Tribulus terrestris (80%). Clinical signs in treatment sheep included dermatitis due to photosensitivity, pruritis, emaciation, keratitis and yellowish mucous membrances. At necropsy, observations included skin lesions, yellowish serosal surfaces and changes in consistency and colour of liver and kidney. Tissue specimens were fixed in 10%. buffered formalin, were stained with H & E stain and examined histologically. Microscopic examination of specimens revealed necrosis of hepatocytes, refractile crystals in bile ducts, epithelial necrosis of bile ducts, bile duct hyperplasia, fibroplasia around the portal triad, infiltration of inflammatory cells. There were necrosis of tubular epithelium in kidney, crystals in renal tubules, infiltration of inflammatoty cells, focal necrosis of cardiac muscles associated with infiltration of inflammatory cells. There were also dermal congestion, infiltration of inflammatory cells in dermis and intraepidermal vesicles and pustules. These lesions were observed with different severity in all six treatment sheep. According to the results of this experiment and comparison with other results of recent studies, it is confirmed that geeldikkop can be induced by feeding of Tribulus terrestris in sheep in Khorasan province.

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