Study of anthelmintic resistance in sheep farms in southwestern Spain. Preliminary results

Gastrointestinal nematode infections cause significant economic losses in sheep farms. Their control is based on use of antihelminthic drugs, but their indiscriminate use accelerates the development of resistance. The objective of this study was to evaluate the presence of resistance to antihelminthics in sheep flocks in Southwestern Spain and to assess management practices that might accelerate its occurrence. For this purpose, 30 animals were selected in each of the 15 farms: Fenbendazole group (n =10), Moxidectin group (n =10) and Control group (n =10). Fecal samples were collected before the application of the drugs (day 0) and 15 days post-treatment to evaluate potential resistance through the fecal egg count tices. The coprological counts showed 4 farms (26.7 %) with reduced efficacy to fenbendazole and 1 (6.7 %) with doubtful efficacy. Regarding moxidectin, 1 farm (6.7 %) showed reduced efficacy and 3 (20 %) presented doubtful efficacy. The survey revealed that 93.3 % of the farms did not perform coprological analysis in the last year, and 100 % opted for treating the entire flock rather than selective treatment. This study highlights the presence of resistance to fenbendazole and moxidectin in sheep in Southwestern Spain and suggests that certain management practices may promote and accelerate this resistance.