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Western Australia worm update - June 2012

Nicole Swan, Swan’s Veterinary Services, Esperance (nicole@swansvet.com):

Not much to report here. We expect an influx of samples in the next month or so as farmers start marking. We have recently had rain though it has also been cold so not great for pasture growth or worms.

We have been seeing quite a few cases of pregnancy toxaemia.

Brown Besier, DAFWA, Albany (brown.besier@agric.wa.gov.au):

With winter comes an increased risk of sheep worm problems, as pasture conditions change to allow worm larvae to survive. Whether worms are a major problem, or no worse than usual, depends on the effectiveness of worm control in summer and autumn.

Worms may be carried through summer in sheep for two main reasons: 

  • Sheep drenched in summer with drenches or autumn that were not fully effective.
  • Sheep considered not likely to be wormy and hence not drenched since last winter or spring.

Drench resistance has been common for many years, but even where relatively new drench types have been used, we can no longer assume full effectiveness (except for the newly-released drench, Monepantel). In WA there is resistance to the most potent Macrocyclic Lactone (ML) drench, Moxidectin, in Ostertagia (Teladosagia) on at least 15% of farms. Resistance has also been found on some farms to the “triple combination” drenches (a white, clear and ML type in one product).

This means that many flocks will have been drenched in summer or autumn with products believed to be fully-effective, but which in fact allowed some worms to survive. These may provide the source of winter worm problems.

Action: we recommend checking faecal worm egg counts of some flocks of all classes in June, except any mobs given known effective drenches within the last 4-5 weeks. If still on generally dry pastures, this will check whether summer drenches (weaners and hoggets) or autumn drenches (adult sheep) have been effective. If the sheep have been on green pastures for the last few weeks, worm burdens could be due to either new worm pick-up, or the failure of earlier drenches.

A worm egg count will indicate whether a drench is needed now (average mob counts over about 250-300epg). If no drench is needed, the counts will indicate whether further monitoring is needed in the short term or can be left for another few weeks. For ewes due to lamb in June or early July, we recommend drenching unless counts are below 200epg.


DownloadDownload the June edition of Western Australia worm update in PDF format (86 KB)