Benzimidazole resistance in equine cyathostomes in Slovakia

The present study included 19 stud farms, including 243 horses, that were i nvestigated for the occurrence of anthelmintic resistant cyathostomes. The number of horses on the farms varied from nine to more than 100, and horses of all ages were included. A minimum of seven horses were used for faecal egg count reduction (FECR) tests. The anthelmintics included were: fenbenda zole (paste formulation), ivermectin (paste formulation) and pyrantel (powd er). Resistance to benzimidazoles was detected on 14 farms, with FECR value s ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment revealed exclusively cyathostome larvae. Ivermectin was tested on eight far ms and proved to be effective on all. Pyrantel was tested on two farms and FECR test indicated high efficacy (92-97%). Egg hatch assay (EHA) results s howed that mean concentrations of thiabendazole that inhibited hatching in 50% of the eggs (ED50) in resistant populations were over 0.1 mug ml(-1). T he results of our study suggest widespread resistance to fenbendazole in eq uine cyathostomes in Slovakia, and possible strategies to delay anthelminti c resistance are discussed briefly. (C) 2000 Elsevier Science B.V. All righ ts reserved.