Control strategies to prevent resistance.

Anthelmintics will continue to play a central role in nematode control programs of livestock for the foreseeable future. However, to prevent the emergence of resistance, anthelmintics need to be either so effective that there are no survivors following treatment or treatment should be so infrequent that those that survive make little or no contribution to subsequent generations of the parasite populations. In this regard, the record for the sheep, horse and particularly the goat industry is not good, whereas the second factor is almost certainly responsible for the lack of a significant resistance problem in the cattle industry. In Australia, where high levels of resistance prevail, control programs designed to limit the increase and spread of resistance have been promoted for some time. However, their development, and certainly their implementation, has tended to be reactive rather than proactive--attempting to deal with the problem when it threatens future productivity, rather than preventing it in the first instance. Regions and/or livestock industries with relatively less of a resistance problem should heed these developments and endeavour to establish a responsible ethos amongst users of anthelmintics. In concert with the general philosophy of Integrated Pest Management (IPM), parasite control schemes should focus on the planned integration of a range of techniques, rather than relying almost entirely on anthelmintics. By these means, sustainable control strategies to prevent resistance could be achieved.