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Tasmania worms, flies and lice update - August 2017

Tasmania WormBoss Worm Control Programs

Tasmania WormBoss Drench Decision Guides





Perth: Paul Nilon, Nilon Farm Health (

The last month has been cold with some showers, but we lack the generalised rain so needed for a good spring.  The soil is bit like meringue: slushy on top but crusty round the edges.  For the time being we will have to be happy with green dust and hope that the south-westerly fronts dump some rain here rather than taking it all to Victoria and NSW.

Lambing is underway, although it will be at a trickle until the start of September.  Most producers have their pre-lambing strategy in place, so we’ll leave it alone.  Worm egg counts (WECs) in merino weaners/hoggets are definitely on the up, with some high counts recorded in all parts of the state.  The question is what trigger [for drenching] to use in these sheep?  If they are in good body condition and have tucker in front of them I suggest that the WECs be allowed to run out a bit in the hope of triggering the young sheep’s natural immunity.  So, let’s say a trigger of 500 eggs per gram (epg) compared with the normal trigger in young merinos of 300 epg.  If they are light and living on hope, drench at the lower trigger.

In July there were two cases of ill-thrift with some deaths in late pregnant ewes caused by mature fluke.  In one case I stopped on my way to the property to photograph a manky drain, thinking this could harbour fluke.  Neither place has a history of fluke, and it’s likely that irrigation has created the right conditions for fluke to cycle.  So, if you have swampy creeks or drains like the one pictured do a fluke check sometime after about March.

One of the places with fluke had an additional parasite problem:  a white capsule failure.  Approximately 60 days after giving the ewes a capsule they were scouring and had an egg count greater than 2000 epg.  A drench test has subsequently shown white drench efficacy at less than 40%

It’s hard to predict capsule efficacy from a standard DrenchTest, but where a drench active has a lower efficacy in a short-acting product (even down toward 60%), it may still provide good effect in a long-acting product provided it is used with an effective primer drench. The primer removes the more difficult-to-kill adult worms, leaving the long-acting product to kill the incoming larvae over the protection period. WormTesting throughout this protection period, as well as an exit drench, is also recommended.

This shows the value of current drench efficacy information, and also shows that sheep under protection of a long-acting product should be monitored for signs of failure.  This is not a criticism: we could all do with a retro-spectroscope.

Here are the WormBoss recommendations for checking the progress of a long-acting product.

  • Where your DrenchTest results indicate that the active/s are effective on your property (i.e. reduced worm egg count by at least 98%) then conduct a WormTest at 30, 60 and 90 days after treatment.
  • If you do not have current DrenchTest results you should do a WormTest at 14, 30, 60 and 90 days after treatment.

In both cases, if it is shown to be ineffective at one of the earlier tests, then the later test/s will be of no value.

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