The role of epidemiological knowledge and grazing management for helminth control in small ruminants.

There is no single requirement more crucial to the rational and sustainable control of helminth parasites in grazing animals than a comprehensive knowledge of the epidemiology of the parasite as it interacts with the host in a specific climatic, management and production environment. In its absence, anthelmintic treatment is either given suppressively, which provokes resistance, or therapeutically, which risks clinical disease and production losses. Sustainable parasite-control programmes require knowledge of seasonal larval availability, origin of larvae contributing to any peaks and climatic requirements for worm egg hatching, larval development and survival. Control measures based on this knowledge include strategic anthelmintic treatments and various forms of grazing management. While these measures can reduce the frequency of anthelmintic treatment required, their effect on selection for drench resistance is more problematical, unless they can be combined with other forms of control to reduce our current dependence on anthelmintics.