Other tools to delay resistance

Grazing management, nutrition and breeding worm resistant sheep are all useful tools to incorporate into a sustainable worm control strategy. Maintaining sheep in a good nutritional state can increase the resilience of sheep to worms. Sheep with good protein and energy levels along with trace elements are better able to resist the effects of worms. The aim of grazing management is to have vulnerable sheep exposed to fewer larvae on the pasture. The result will be that fewer drenches will need to be used. At the same time grazing management provides nutrition to allow sheep to better deal with parasites. Breeding sheep that are better able to resist worm infections will help to reduce the number of drenches used and hence slow the development of resistance. Breeding for worm resistant sheep will take time. Experts suggest it will take 10–12 years of consistent selection to significantly reduce the FEC of weaners to the point where they require fewer annual drenches.

“Nutrition is absolutely critical. It doesn’t matter how good the drenches are, if you stress young Merino sheep then you’re going to have problems with lack of immunity and susceptibility to reinfection.” Dr John Evers, Rural Lands Protection Board Young, NSW