Anthelminthic resistance of Haemonchus contortus in small ruminants in Switzerland and Southern Germany

Summary Two goat and two sheep flocks have been found to be suspicious of a clinically evident reduced anthelmintic efficacy, i.e. lacking improvement of gastrointestinal disorders, insufficient weight gain and continuing inappetence after anthelmintic treatments. In order to conduct an appropriate evaluation of the efficacy the following trials were performed: the faecal egg count reduction test on the studied goats of the two herds revealed a reduction of the egg-excretion after the eprinomectin-treatment (1 mg/kg BW, pour-on) of 17.4% and 27.5%, respectively, which clearly confirms the occurrence of anthelmintic resistance against eprinomectin in these two herds. The alternatively administered moxidectin-treatment (1 mg/kg BW, pour-on) of one flock resulted in a 99.1% faecal egg count reduction. In both sheep flocks, 30 randomly selected sheep were divided in three groups and each group was treated with a different anthelmintic, according to the instructions for use. The faecal egg count reductions for the various groups treated orally with benzimidazoles were 70.8% and 55.3% (albendazole), 52.4% (fenbendazole) and 47.3% (oxfendazole). The two moxidectin-treated groups (0.2 mg/kg BW, oral) showed an EpG-reduction of 100% and 44.3%, respectively, thus also demonstrating resistance against macrocyclic lactones. Pre- and post-treatment faecal larval cultures revealed Haemonchus contortus as the predominant resistant species.