Chemical resistance and residues

Chemical resistance is very common in livestock parasites, and it doesn’t take long before resistance against a new chemical emerges.

Problems caused by parasites are usually a due to a combination of parasite, animal, environmental and management factors. As a result, relying on chemicals alone to control parasites is not sustainable and can lead to chemical resistance.

This is why producers need to 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 food safety reputation is underpinned by our ability to meet these demands.

Only use chemicals (dips, drenches, back-liners, etc.) when necessary as part of a parasite control program. Follow all  label directions and restrictions and use personal protective equipment. Also be aware of:

• withholding periods (WHPs)
• export slaughter intervals (ESI)
• re-handling intervals
• the safe disposal of empty containers and unused product.

Record all animal treatments 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 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 (Drench Test) or a faecal worm egg count 10-14 days after treatment (Drench Check).

Strategies to minimise drench resistance include:

• treating introduced livestock on arrival with a quarantine drench and keeping them in a quarantined for 24-48 hours before allowing them to join the rest of the flock/herd
• requesting an animal health statement when purchasing livestock so that 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, as determined through the use of regular (every 2-3 years) drench resistance tests (Drench Test or Drench Check)
• rotating drench groups, including combination drenches, to avoid relying on only one chemical group
• drenching only when needed
• regularly monitoring the worm status, particularly in 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 the 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 the selection of Australian Sheep Breeding Values (ASBVs) for low worm egg count and dag score within selection for important production traits for sheep.