Monitoring of anthelmintic resistance in small strongyles in the Czech Republic in the years 2006–2009

The aim of the field study performed in 2006 was to investigate the occurrence and distribution of intestinal helminths in horses based on pre-treatment faecal egg counts. In total, 948 horses bred on 37 farms were tested. Thirty six (97.2%) farms tested were positive for cyathostomins; horses in 9 (24.3%), 6 (16.2%) and 1 (2.7%) different herds tested were positive for Parascaris equorum, Anoplocephala perfoliata and Strongyloides westeri, respectively. In 21 herds, 344 horses with values exceeding 100 eggs per gram were included in the trial for the presence of drug resistant cyathostomins by a faecal egg count reduction test. Horses were treated orally with recommended doses of fenbendazole and ivermectin. Resistance to fenbendazole was detected on 20 farms (95.24%) with values of faecal egg count reduction test ranging from 0 to 90%. Ivermectin remained effective in all tested herds with the value of faecal egg count reduction test 96–100%. In autumn 2008, 178 horses on 10 farms were examined. Of these, only seven horses tested were negative for cyathostomins. One farm was tested positively for Anoplocephala perfoliata, and one for Parascaris equorum. In spring 2009, six farms were examined, four of which were the same farms as in 2006. We found a decreased number of eggs per gram in all horses, but an increase in benzimidazole resistance, which was found in 5 farms out of 6 (faecal egg count reduction test 15.2–84.6%). This is the first wide survey in horses from the Czech Republic. Based on this study, we can conclude that benzimidazole resistant cyathostomins in horses are widespread but ivermectin is still fully effective