The productivity of Merino flocks in South-Eastern Australia in the presence of anthelmintic resistance

Nematodes resistant to the benzimidazoles and levamisole anthelminitics have been present in many sheep flocks in South-Eastern (SE) Australia for over 20 years. We examined the productivity and profitability of six self-replacing Merino flocks, in which resistance to these anthelmintics had been confirmed for over 10 years. The profitability of three farms increased considerably over this period following progressive adoption of known determinants of profitability, namely the optimum application of fertilisers, increased stocking rates and improved sheep genotype. The remaining three flocks maintained their physical production and profitability, with two of these considerably increasing the scale of their enterprise. This suggests that anthelmintic resistance needs to be kept in perspective and tackled as just one part of whole farm management.