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In the November 2014 edition of ParaBoss News there was an incorrect report regarding drench resistance to monepantel (the active in Zolvix®).

The current known drench resistance status of monepantel in sheep is:

  • Resistance has NOT been detected in sheep flocks in Australia and monepantel remains an effective treatment option.


WormBoss recommends that effective treatments for roundworms in sheep reduce worm egg count by at least 98% as shown by a DrenchTest.

Establishing the efficacy of drench actives by conducting a DrenchTest every 2–3 years is essential for good worm control practice. In between times, do regular DrenchChecks.

The principles for using drenches (in order of priority) include:

  1. Use effective drenches: these are known to reduce the worm egg count on your property by at least 98% as shown by a DrenchTest. The more effective the drench, the fewer the drench-resistant worms left in the sheep after treatment.
  2. Use a combination of two or more actives where possible, as fewer worms are able to resist more than one active at a time.
  3. Use short-acting treatments where possible, and restrict the use of persistent products for specific purposes and high worm-risk times of year.
  4. Rotate among all effective drench groups each time a mob is drenched (and for each paddock where possible).

In addition, it is important to keeping drench-resistant worms out of your property by quarantine drenching all sheep new to the property.

  • Use a combination of no less than 4 unrelated drench actives, with at least one of these being monepantel (Zolvix®) or derquantel (with abamectin—Startect®). 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.
  • Quarantine the sheep after treatment.