Drench resistance testing - Elders Rural Services

Drench resistance testing

A study by MLA in 2019 reported that gastrointestinal worms cost the Australian sheep industry $450 million dollars annually.

To ensure that you are minimising production losses you need to use drenches that are as effective as possible. The best way to do this is by conducting a drench resistance test every 2 to 3 years.

What is drench resistance?

Drench resistance occurs when a population of worms are no longer susceptible to a lethal dose of a specific drench active. Normally only a small portion of the population may survive, but over time, if they are repeatedly exposed to the same drench, the resistant worms will have more and more opportunity to breed. This results in the worm population having a higher level of resistance and the drench with a lower level of efficacy.

Fortunately, as a state, Western Australia are currently sitting in a much better position than the eastern states. However, we still need to act now to slow the resistance. For example currently in WA Abamectin only has an efficacy of 80.9 per cent against Barbers Pole worm and Moxidectin is only 86.7 per cent effective against Brown Stomach worm.

Worm control

To best manage worms on your property:

  • Start by conducting a drench resistance test to work out which drenches are the most effective (>98% efficacy).
  • Implement strategic grazing systems (smart grazing linked below)
  • Use worm egg counts at key points within the year; and
  • Only drench when required.


Drench resistance testing can be organised with your local Elders animal health representative.

Find your local branch

Article written by Ella-Jane Bird, animal health and rural products specialist at Elders Cranbrook WA.

The information contained in this article is given for the purpose of providing general information only, and while Elders has exercised reasonable care, skill and diligence in its preparation, many factors (including environmental and seasonal) can impact its accuracy and currency. Accordingly, the information should not be relied upon under any circumstances and Elders assumes no liability for any loss consequently suffered. If you would like to speak to someone for tailored advice relating to any of the matters referred to in this article, please contact Elders.

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