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Western Australia worm update - March 2012

Brown Besier, DAFWA, Albany (

Dry conditions mean few worm problems at this time of year, but getting worm control right in autumn is essential to avoid problems in winter and spring.
We now recommend that adult sheep are drenched in mid-autumn (ideally the first 2 weeks of April), not in summer. We have known for some years that summer drenching is a major cause of drench resistance, as only resistant worms survive and these are the source of future worm populations. Delaying the drench until autumn allows a small number of worm eggs to develop to the larval stage, as egg development usually starts in early March, and as these are from “less-resistant” worms (haven’t had recent drench exposure), there is little risk of rapid increases in resistance levels.


Adult sheep: Drench all mobs with a fully-effective drench between the end of March and mid-April, or do worm egg counts on adult sheep mobs, and drench any above about 200 eggs per gram (most will be, but some may not warrant a drench).

Weaners, hoggets: These should have received a summer drench, but are you sure it has worked? Unless the summer drench used is known to be fully effective, there may be enough surviving worms to fuel heavy worm burdens in winter. A worm egg count in mid-autumn is good insurance – an extra treatment may be needed.

Nicole Swan, Swan’s Veterinary Services, Esperance (

Mobs tested in the last few weeks have had varying results.

Counts have varied from 5-350epg average, with individual counts ranging from 0-1050epg.

Farms with higher counts have in most cases been coastal properties. In these cases drenching with a Closantel based drench to kill Barber’s Pole and provide residual protection has been recommended even in their mobs with lower counts. Overall the recommendation for mobs with high counts has been to use Q-drench and in those with low counts to use Closantel if they are in a high risk Barber’s Pole area.

We are recommending that farmers do a WEC to determine if drenching is required prior to the break. This is usually late March.

For March 2012 state outlooks, please follow the links below:
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