Resistance of Haemonchus contortus to thiophanate

The occurrence of a field strain of Haemonchus contortus which was resistant to thiophanate and susceptible to thiabendazole and levamisole is reported. The LD95 of thiophanate for the strain was found to be 156.1 mg/kg and its resistance factor was 6.7. In possessing specific thiophanate resistance it differed from previously reported thiophanate resistant strains of H contortus which have been benzimidazole resistant worms that have possessed cross resistance to thiophanate.