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Western Australia worm update - August 2012

Nicole Swan, Swan’s Veterinary Services, Esperance (

We have had fairly consistent rain in the last month, together with some sunny warmer days (20-22°C)

Most worm counts have been low however we did see a case yesterday where there were deaths in a mob of 300 ewes. The unwell ewes had watery scours with a corrected WEC of about 2500epg.

These ewes had been drenched less than 90 days ago (26/5/12) with Cydectin LA. We then did 9 WECs from the mob of which 5 had positive counts with an average of the 9 samples of 120epg.

These ewes will be drenched next week at marking as will the lambs as a number of them are scouring badly. We plan to do a FECRT (resistance test) on some undrenched (except for Closantel) lambs from this mob when they are a few weeks older to determine the efficacy of Cydectin on this property.

Brown Besier, DAFWA, Albany ( )

Winter worm worries in ewes
Reports of severe worm problems continue to come in, especially of ewes. I’ve seen more dirty backsides in ewes recently than for some years, and there can be a real risk of losses of ewes in light condition.

In increased worm problem is likely to be due to two major reasons:

  • The carry-over of worms from last summer, when we saw unusually high worm burdens for that time of year after the heavy December rains. Weaners had especially heavy worn burdens, and drenches that were anything less than 100% effective would have allowed more than the usual number of worms to survive, and therefore lead to higher levels of pasture contamination with worm eggs in autumn and winter. We are now seeing the results in a higher intake of worm larvae, in all classes of sheep.
  • The temporary loss of immunity of ewes to worms over lambing time. For about 2 months after the birth of a lamb, ewes become much more susceptible to worms, with more worm larvae taken in developing to adult worms, and existing worms laying more eggs. This is seen as higher worm egg counts than before lambing, and the heavier worm burdens can lead to severe scouring and occasionally ewe deaths. The situation corrects itself in time, as immunity returns after a few weeks, and worm egg counts usually drop to low levels by weaning time.

Immediate action: If there are signs of severe scouring in more than a few ewes (some are genetically programmed to be more worm-prone), a drench may be needed – ideally when the lambs are in for marking. If scouring is not seen until after marking, the decision is whether the signs are so severe than it is worth re-mustering.

Otherwise, the decision is whether a drench is necessary when they are yarded for lamb weaning or crutching – often counts will be back to low levels by then, and no drench is warranted. A worm egg count is the only way to tell.

Prevention: This comes back to effective drenches at critical times: in summer for weaners and hoggets, and in autumn for ewes. For ewes lambing from mid-June onward, a pre-lamb drench may be needed – again, this can only be indicated with a worm egg count as often ewe counts are still very low.

A drench resistance test is a good investment to ensure the drenches work when they need to – more news on resistance testing next month.

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