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South Australia worms, flies and lice update - May 2017

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Recent faecal worm egg counts (WormTest) indicate modest worm burdens mostly in pregnant ewes. This likely reflects the good condition of ewes following the above average summer/autumn feed quality and quantity around the State combined with recent mild conditions.

The soil moisture reserves have allowed crops to be sown in April/May and further rainfall in mid-May will have encouraged both croppers and graziers given the below average rainfall forecast for winter.

Ewe condition and feed on offer should limit significant worm burdens going into winter, but the situation can soon change as pasture growth slows and increasingly close grazing encourages worm larval pickup. Limited monitoring at this time of year probably reflects the preference of many producers to drench ewes pre-lambing rather than risk a significant worm burden developing during lambing.

During winter the majority of the worm population is more likely to be surviving on pasture as larvae rather than as immature and adult worms in the gut. The consequence is that the choice to drench pre-lambing has little consequence on the development of drench resistance as any worms that develop drench resistance will be grossly diluted by the “chemically unexposed” or drench sensitive worm larvae on the pasture.

You should already be preparing low worm risk paddocks for weaning given that worm larvae do survive on pasture for several months over winter. Paddocks intended for weaners are best either left ungrazed from autumn, or only grazed by sheep known to have minimal worm risk to promote adequate high quality feed by weaning.

It is also best to plan now to do a drench resistance test at weaning to check the efficacy of the various drench groups and decide the drench use program for the next two years. Contact your animal health advisor to arrange this if you need assistance.

Note: as a general statement the situation described above applies similarly to other ‘pseudo-ruminants’ such as goats and alpacas, but limited access to faecal egg count monitoring in these species limits the opportunity to provide specific comment.

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