Introduction: The study of the parasite-species occurring in a region is of paramount important for planning an efficient control program and to delay resistance to anthelmintic compounds. Jargalan, northeast of Iran, comprises a total of 14 villages and is the most important source of Turkmen horses in Iran. Material and Methods: To study the parasitic infestation of Turkmen horses in this region, faecal and blood samples collected from 46 (30 male and 16 female) randomly selected healthy Turkmen horses (about 10% of population and at least 2 horses from each village). All horses had no previous anthelmintic treatment or had an irregular treatment with very low doses. Faecal egg counts (Clayton lane method), faecal culture, modified Knot test, differential blood cell count and measurement of blood PCV, RBC indices, fibrinogen and total solid of plasma were performed. Results: No microfilaria was observed in blood samples. Nematode eggs (Cyathostomidae) were found in 26 faecal samples (0-650 eggs/gr, 62± 145). There were no significant correlation between age, blood parameters and anemia with the severity of infestation. No significant difference in the severity of infestation was found between treated and untreated groups. But a significant difference was found between male and female groups of horses (P = 0.046). It seems that difference in housing is the probable cause of this difference. Conclusion: Probable causes for found parasitic spectrum (climate, regional parasite spectrum, age of horses etc.) are discussed in this paper.

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