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South Australia worms, flies and lice update - May 2015

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

Adelaide: Colin Trengove, Sheep Health Lecturer (UA Roseworthy campus) (

The season has progressed well to the north of the River, but feed remains lean to the south. Correspondingly, worm egg counts have generally been low in well fed ewes with approximately a quarter of recent monitoring indicating a need for a drench. This highlights the need to assess ewe condition score and feed on offer as well as WEC in the lead up to lambing in order to make the best decisions about worm control. Ewes in good condition i.e. score 3, can generally keep worm burdens suppressed and provided feed is not limiting there is little reason to drench prior to lambing.

If there is a need to drench at this time of year the choice of drench is not so critical, as like dog fleas, the majority of the population is in the environment rather than the host. A drench is likely to have a limited benefit as worm larvae ingested from the pasture are likely to soon replace the worms removed by the drench. Pastures are unlikely to be worm-free in early winter as most will have been grazed and contaminated recently due to the lack of feed on offer over autumn. 

Once lambing is underway, WEC monitoring performed at marking will indicate whether a drench is required before or at weaning. Lambs usually only receive their first drench at weaning to ensure they can achieve best growth rates thereafter. In this case the most effective drench is preferred. A weaning drench onto the best quality low worm risk feed will ensure the weaners get the best start.

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