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Abstract
The present study included 19 stud farms, including 243 horses, that were investigated
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: fenbendazole (paste formulation), ivermectin (paste formulation)
and pyrantel (powder). Resistance to benzimidazoles was detected on 14 farms, with
FECR values ranging from 65.1 to 86.3%. Larval cultures after fenbendazole treatment
revealed exclusively cyathostome larvae. Ivermectin was tested on eight farms 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 showed that mean concentrations
of thiabendazole that inhibited hatching in 50% of the eggs (ED(50)) in resistant
populations were over 0.1 microg ml(-1). The results of our study suggest widespread
resistance to fenbendazole in equine cyathostomes in Slovakia, and possible strategies
to delay anthelmintic resistance are discussed briefly.