Introduction and goals: Malignant Ovine Theileriosis (MOT) is one of the most important tick-borne disease caused by Theileria lestoquardi among small ruminants. It is distributed from Mediterranean region to China. According to many references, goats are resistant to malignant theileriosis. The study was carried out to compare the clinical signs and parasitological findings in sheep and goats after being experimentally infected by T. lestoquardi. Material and methods: In an experimental study, T. lestoquardi infection, was transmitted to a goat and sheep by infected Hyalommaanatulicumanatulicumticks. The hosts were clinically examined. Blood and lymph nodes smears werecollected during the study. Results: The sheep and the goat showed clinical signs including fever, pre-scapular lymph nodes enlargement, anemia and mucosal membrane pallor. After 12 days post infection (PI), body temperature in the goat rose to 40.5℃ while the temperature for the sheep was 42℃. Pre-scapular lymph nodes enlargement was notable in the sheep than the goat but the goat showed earlier and more severe mucosal membrane pallor during study. The parasitemia was 2% in the infected goat and 2.8% in the sheep on day 12 PI. The infected goat showed better response to Buparvaquonetreatment compare to the sheep so that after 3 months post infection, it was difficult to find piroplasmsin the goat blood smear while they were still detectable in blood smear of the infected sheep. Discussion and conclusion: According to our findings, goats are more resistant to theileriosis than sheep and it seems that goats can reducethe virulence of theileriosis among small ruminants.

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