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  • Writer's pictureASHEEP

Wormboss in Esperance - Worm Egg Count Resistance Testing Report

The Wormboss Project is being run in the Esperance Region between 2018 - 2019 and gives local producers an opportunity to learn more about drench resistance, testing, and what it might mean for their flock.

In late 2018 a local Esperance producer was tested and the following information provides a summary of the results on their flock. The report is from a mob of ewes with an average age of 9 months in condition score 2-4, there had been 30mm rain in the 30 days before testing and they had never been drenched previously.

# Note: Derquantel does not come in a single active formulation.

What does this mean for your future-drenching program?

Black Scour Worms (Trichostrongylus)

Albendazole, levamisole and napthalaphos all had reduced to nil efficacy against these worms. All the other actives tested were fully effective against these worms. Future use of combinations containing any of these effective actives is recommended to ensure control of this worm when drenching.

Small Brown Stomach Worms (Teladorsagia)

All actives, apart from Zolvix, has reduced to nil efficacy against these worms. Most combination drenches contain mixes of these actives which also calculate as having

much reduced efficacy. Although Startect has reduced efficacy against these

worms the nature of this combination drench means that this efficacy should stay at this level for the foreseeable future. With this in mind a drenching program where Zolvix and Startect are rotated will be a viable option for this property.

General principles of drench use are:

1. Drench when necessary i.e. when worms are likely to impact health or productivity of the sheep- use worm egg counts to check and monitor worm burdens.

2. Use effective drenches i.e. ones that have >95% efficacy against the worms present- use drench tests to check efficacy.

3. Use combinations instead of single active drenches whenever practical.

4. Use non-chemical means to control worms including paddock rotation, rotation with cattle, cropping or haymaking or pasture spelling to reduce the larval worm burden.

5. Use short-acting drenches instead of long-acting drenches unless paddocks are heavily contaminated and other solutions are impractical.

6. Quarantine drench all newly-introduced sheep with drenches that contain four active ingredients, including one of the new ones (derquantel or monepantel). In practice, this means drenching with either Zolvix Plus (monepantel + abamectin) or Startect (derquantel + abamectin) as well as a BZ + Levamisole combination such as Duocare or Scanda. Don’t mix the two drenches, just drench once with each drench.

The Wormboss Project runs until the end of 2019. For more information contact


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