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Don't import drench resistance

Stephen Love, State Coordinator - Internal Parasites, NSW DPI, Armidale
September 2012


There are two ways you can get drench-resistant worms: breed your own and/or buy someone else's.

Here is advice on quarantine treatments from the revised material developed for the new WormBoss (to be launched soon):

  • Keeping drench-resistant worms out of your property is part of sustainable worm control.
  • Assume that purchased sheep are carrying worms with some degree of drench resistance to one or more drench groups.

1.   Quarantine drench all sheep new to the property.

  • Use a combination of no less than four unrelated drench actives, with one of these being monepantel (Zolvix). This can be done using multi-active (combination) and/or single-active products concurrently: up the race with one product, then up the race again with the next.
  • Do not mix different drenches unless the label states you can, as different products may be incompatible.

2.   Quarantine the sheep after treatment.

  • Hold the sheep in quarantine in yards (small mobs) or a secure paddock (larger mobs) for at least three days to allow worm eggs present at the time of drenching to pass out of the gut.
  • Provide adequate feed and water.
  • Keep this paddock free of sheep, goats or alpacas for at least three months in summer or six months in cooler months.

3.    After quarantine, release the sheep onto a paddock that is likely to be contaminated with worm larvae due to grazing by other sheep. This will dilute (lower the proportion of) resistant worms surviving treatment with worm larvae already on your property.

4.    WormTest the imported sheep 10–14 days after drenching for added confidence that treatment was successful.

5.    Get expert advice on up-to-date recommendations for quarantine treatments. These will  evolve as the drench resistance picture changes.

Monepantel and Derquantel each represent new drench groups. In Australia, monepantel was released in September 2010 as Zolvix®. Derquantel is not yet released in Australia.