ABSTRACT

This survey was carried out on a horse farm in order to acquire recent data on macrocyclic lactone‐resistant Parascaris equorum which had been previously detected on this farm and to determine efficacies of ivermectin and pyrantel against strongyles in order to determine whether a resistance problem also exists in these parasites. In the first part of the study, abamectin was given to horses infected with P. equorum. In 11 out of 12 horses, zero efficacy (0%) was seen against P. equorum. Subsequently, horses which were Parascaris‐positive after abamectin treatment received pyrantel pamoate and its efficacy was 0‐80% in 3 animals and 96‐100% 8. The remained Parascaris‐infected horses were treated again with a double dose of pyrantel and it was fully effective in all horses. In the second part of the study, efficacy of ivermectin and pyrantel against strongyles infections was assessed 14 and 28 days after treatment and an efficacy of 100% was detected on both days. In conclusion, macrocyclic lactone anthelmintics were found to be non‐efficacious against P. equorum whereas pyrantel at the double dose rate was effective against these resistant worms. Resistance to ivermectin or pyrantel was not detected in strongyles.