Chemical resistance and residues

The emergence of chemical resistance is increasingly common in livestock parasites.

Relying on chemicals alone to control parasites is unlikely to be sustainable in the long-term because of the potential for chemical resistance to develop and because parasites are not the sole cause of the problem. Problems caused by parasites are usually a combination of parasite, animal, environment and management factors. Focusing only on the parasite and failing to address the other factors will produce only short-term results.

Producers should adopt an integrated approach to parasite control.

Australia's red meat markets demand that products from farms be free of unacceptable chemical residues. Australia's ability to meet these stringent demands underpins our excellent agricultural and food safety reputation.

When using drenches, pour-ons and other chemicals strategically as part of an overall parasite control program, producers must read the label thoroughly before use. Follow all label directions or restrictions, including directions for dose rates, safety precautions, personal protective equipment, withholding periods (WHPs), export slaughter intervals (ESI), re-handling intervals and disposal of empty containers and unused product. Record the appropriate information and include on the LPA NVD/Waybill if the livestock are sold.

Drench resistance

Drench resistance is widespread in all sheep growing regions in southern Australia. Drench resistance is also common in goats and has recently been reported in cattle. Producers should know the drench resistance status of the worms on their property. This is achieved through the use of regular (every 2-3 years) drench resistance tests.

Strategies to minimise drench resistance include:

  • Always quarantining introduced livestock and treating them with a quarantine drench.
  • Always requesting an animal health statement when purchasing livestock so you are aware of the disease status level of assurance that is being provided by the livestock vendor.
  • Using drenches strategically as part of an overall parasite control program.
  • Reading labels thoroughly before use and following the directions for dose rates.
  • Using effective drenches, determined to be effective through the use of regular (every 2-3 years) drench resistance tests.
  • Rotating drench groups, including combinations, to avoid relying on only one chemical group.
  • Drenching only when needed.
  • Monitoring the worm status of the flock regularly, particularly high-risk mobs such as weaners and pregnant females.
  • Using only those products that are registered for use in the livestock being treated.
  • Using grazing management to reduce exposure of young livestock to heavily contaminated pasture.
  • Ensuring livestock maintain body condition targets.
  • Improving nutrition to increase the resilience and immunity of livestock to worms.
  • Including selection ASBVs for low worm egg count and dag score with selection for important production traits for sheep.

More information

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