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Western Australia worm update - November 2013

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

Things are now starting to dry off. There are still rainy days which are frustrating some of the grain farmers. Despite our really wet year we have seen few worm disasters.


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

The past month has seen some very high worm burdens across the state, leading to several reported cases of lamb losses. A number of people who do their own worm egg counts have seen counts far higher than ever before, causing them to wonder whether they are seeing Barbers Pole worm (which produces very high egg counts even with moderate worm numbers). The answer is usually “no, in extreme cases we do see average mob counts of 2000 – 3000 eggs per gram – though often accompanied by sheep deaths”.

The causes for the current high worm levels occurred months ago, with the early break to the season that allowed worms to cycle earlier than normal. In many cases, worm problems now will be linked to drench resistance – the failure of Summer and Autumn drenches to completely remove worm burdens at the time, so the worm populations started from a higher base than if the drenches were fully effective.

Fortunately, harvest is underway in most parts of the state, giving the opportunity for a quick solution: drenching lambs or hoggets onto crop stubbles completely removes the threat of worms (provided the drench works). Where stubbles are not yet available because harvest hasn’t started, there will generally still be some worm larvae on pasture, and if a drench is given now, a Summer drench may still be needed later. A worm egg count will indicate whether a drench is needed urgently, or whether it can be delayed until pastures dry off. Don’t be caught with worm problems just because you usually would not have drenched at this time in most years!

We don’t recommend drenching ewes in Summer: they should receive a drench in Autumn, as Summer drenching all sheep on the farm is a quick way to develop drench resistance. However, a worm egg count may be worthwhile if you have had worm problems this year, as in some cases higher burdens than usual can develop in adult sheep.

Finally – it is not too late to do a drench resistance test if lambs have not yet been drenched!