Principles

Wormwise Agreed principles

  • Healthy animals harbour worms and always will – eradication is neither an appropriate goal nor achievable.
  • Well-fed animals are less affected by worms than those under nutritional stress.
  • Older animals are generally less susceptible to worms than younger ones, and, at times, can be used to reduce the number of infective larvae on pastures.
  • Animals vary in their susceptibility to parasites (genetic variability).
  • Animals can be selectively bred for resistance to roundworms.
  • Each farm is unique and effective worm management may be different from farm to farm.
  • When breeding for a characteristic, increased selection pressure will result in more rapid change being made (applies both to livestock and parasites).
  • Most of the year there are more worms, in the various life stages, on pasture than inside the animals.
  • Anthelmintics are a finite resource. The way in which you use drenches and manage parasites can change the rate at which you select for resistant worms.
  • Long-acting drench formulations may hasten development of drench resistance.
  • Once present on a farm, resistance to anthelmintics can be considered permanent.
  • Effective combination anthelmintics may help delay the onset of resistance but the benefit may be lost if resistance to the individual components is already advanced. A population of susceptible animals (i.e. a refugia) should be maintained on farm. Farmers need to ensure they are using a drench that is effective on their farm.
  • Every farm should maintain a parasite management plan, developed in conjunction with their trusted parasite advisor.

Key points

  • Parasitism is a major cause of loss of production in livestock.
  • Based on current information, it is clear that many New Zealand farmers are using anthelmintics in a manner that will result in drench resistant parasites and drench failure.