THE EFFECTIVENESS OF BENZIMIDAZOLE-LEVAMISOLE COMBINATION DRENCHES INTHE PRESENCE OF RESISTANCE TO BOTH BENZIMIDAZOLE AND LEVAMISOLE ANTHELMINTICS IN NEW-ZEALAND SHEEP

Examination of 25 cases of multiple benzimidazole and levamisole resis tance, identified in sheep by faecal egg count reduction testing at th e Batchelar, Lincoln and Invermay Animal Health Laboratories, showed t hat benzimidazole-levamisole combinations provided effective control i n eight (47%) of 17 cases in which they were tested. Overall, the use of combination drenches resulted in average improvements in faecal egg count reductions of 25.6% (p<0.01) and 23.2% (p<0.05), respectively, over those achieved by the use of benzimidazole or levamisole drenches alone. The results suggest that instances of multiple resistance in w hich combination drenches might be effective are unlikely to be predic table either by identification of the parasites involved, or from the levels of benzimidazole or levamisole resistance present.