Preventive control programmes for nematode infections of sheep, which depend upon strategically timed treatments of anthelmintics, are based on epidemiological knowledge of the time relationships between contamination of pastures and seasonal availability of infective larvae in different climatic regions. In Australia by the time these programmes were being actively promoted resistance to two of the three families of anthelmintic drugs had already emerged. A high prevalence of resistance is now widespread in Australia and measures for the management of resistance have been incorporated into recommendations of worm control. These include, a reduction in frequency of treatments, elimination of underdosing, assessment of effective drugs, their use at high dose rates in an annual rotation and the integration of treatment with grazing management. Nevertheless, there is concern that preventive control programmes may not be sustainable over the long term. Increased attention is now directed to alternative means of control, such as vaccination of sheep against nematode infections and breeding sheep with enhanced resistance to infection. The integration of these measures into preventive control programmes and the extent to which they can replace chemotherapy are topics for ongoing study.
Proceedings of the New Zealand Society of Animal Production, Volume 50, , 155-160, 1990
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