Recent developments in the management of anthelmintic resistance in small ruminants – an Australasian perspective

There have been a number of significant advances in recent years to the theory and practice of managing anthelmintic resistance in sheep in Australasia. The general principles of resistance management are, firstly identification and mitigation of high-risk practices, secondly using effective anthelmintics, and thirdly maintaining a refuge of unselected parasites. The first of these principles has been updated recently with the findings from a series of farm-based trials in New Zealand, in which the economic benefits of both short- and long-acting anthelmintic treatments in ewes pre-lambing were found to be inconsistent and not always positive. There have also been significant changes to the second principle, particularly given the introduction of new active families onto the market. Evidence continues to favour the use of combination products to maximise efficacy and delay the onset of treatment-failure. Many farmers have readily accepted the effectiveness of maintaining a refuge of unselected parasites; the challenge for researchers and advisers is now to improve adoption of properly designed and implemented resistance management programmes. A recently completed education programme in New Zealand has demonstrated that when this is achieved, then anthelmintic resistance can be controlled, and in many cases reduced in severity.