Benzimidazole resistance in cyathostomin populations on horse farms in western Anatolia, Turkey.

A cross-sectional survey was performed on ten stud farms in western Anatolia, Turkey, in order to provide the first information on the problem of anthelmintic resistance in equine strongyles in this country. Benzimidazole (BZ) resistant cyathostomin populations were detected on seven farms if pre- and post-treatment egg counts are compared in treated animals and the resistance is defined as a mean faecal egg count reduction (FECR) of <95% with a lower 95% confidence limit of <90%. Egg hatch tests using an ED(50) of 0.1 microg/ml thiabendazole as the cut-off value confirmed BZ resistance on four of the seven farms. The probable reasons for the occurrence of BZ resistance are discussed. Resistance to pyrantel embonate or macrocyclic lactones, evaluated on five and six farms, respectively, was not detected using the FECR test.