OCCURRENCE OF LEVAMISOLE-RESISTANT AND TE TRAMISOLE-RESISTANT GASTROINTESTINAL (GI) NEMATODES IN SHEEP

Two experiments were carried out with sheep naturally infected with ga strointestinal nematodes to evaluate efficacy of anthelmintics using i n vivo faecal egg count reduction (FECR) test. In experiment 1 with 28 ewes, the following efficacy of anthelmintics given at recommended do se rates was observed: albendazole 99.4%, ivermectin 99.3% and levamis ole 81.8%. In experiment 2 with 18 ewes, tetramisole exhibited 71.3% e fficacy. Suspected resistance to imidothiazole anthelmintics was confi rmed by in vitro larval development test (LDT)-minimal inhibition conc entration (MIC) values were estimated at 2.0 mu g/ml. Infective larvae L3 cultivated from eggs produced by the population of resistant helmi nths were identified as Ostertagia and Trichostrongylus spp.