Sheep worms which are resistant to chemical drenches have been detected with increasing freuency is Western Australia\u27s south-western farming areas between 977 and 1980. These worms have anthelmintic resistance and such genetis resistance puts essential internal parasite control practices at risk.
This prompted veterinarians in the Esperance, Albany, Bunbury, Geraldton and Northam areas to survey farms to determine the prevalence of resistance to drenches and to define those sheep management practices which encourage its development.
This article describes the survey which was conducted to assess the extent of drench resistance, what causes its build-up and how it can be controlled by using a combination of drenching programme changes and sheep management practices.
It has been estimated that drench resistance alone could cost the State\u27s sheep industry 4millionto6 million a year in lost production, and, as shis survey shows, there is potential for far greater costs if resistance continues to increase
