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.
- 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.