Anthelmintic resistance in New Zealand

Anthelmintic resistance in New Zealand
Peer reviewed


Anthelmintic resistance was first confirmed in New Zealand in 1979 and since then has become common-place; more than 50% of sheep farms now have detectable levels of resistance to one or more chemical classes of anthelmintic. Farmer drenching practices have changed little over the last 15-20 years and are clearly exerting a significant level of selection for resistance. In the absence of new chemical classes of anthelmintics, current parasite control practices will be unsustainable in the long-term. Once substantial resistance has developed, significant reversion to susceptibility is unlikely and re-introduction of failed drugs is likely to result in the re-emergence of control problems. The number of anthelmintic treatments applied is not necessarily a reliable indicator of selection pressure and should not be the onle factor considered in strategies for minimising the development of resistance. The relative potential of the different anthelmintics now available, particularly the longacting roducts, to select for resistance varies with the way they are used and with other epidemiological and management factors; generalisations about their respective roles in the development of resistance are often unreliable. In many cases, literal extrapolation of recommendations for the management of resistance from Australia to New Zealand is unsupportable, given the differences in climate, parasite ecology and farming practices between the 2 countries. In the absence of a refuge for susceptible genotypes, as occurs when anthelmintic treatments are used as a means of generating low-contamination ‘safe’ pasture for young stock, the rapid development of resistance is likely. Anthelmintic treatments applied to animals with a high level of immunity, or which become immune while the anthelmintic is active, are likely to select for resistance faster than treatments applied to non-immune stock.

Access to the full text of this article is available:

through another providers website:

If you're a member or subscriber and believe you should have access:



Register for an account

Request new password

The whole of the literary matter of the New Zealand Veterinary Journal is copyright Taylor and Francis, Downloading this article signifies agreement with the terms and conditions of electronic access.