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South Australia worms, flies and lice update - April 2021

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

The exceptional dry start to the year continues as promises of rain across the agricultural areas either dissipate or fail to deliver a significant amount. However, worms take little notice and counts in the hundreds are common in carryover lambs and some adults — especially in the southeast.

Ewe mobs represent a relatively small proportion of total worm egg count (WEC) monitoring over the last month despite early lambing being underway. This highlights the widespread practice of drenching ewes pre-lambing as a routine risk mitigation, rather than monitoring to assess the need for drenching. A substantial reduction in chemical use and drench resistance could be achieved if flock managers were more focused on preparing low worm-risk pastures for lambing ewes combined with monitoring WECs more frequently. While requiring more diligence, this strategy is a great opportunity to reduce dependence on chemicals and adopt a more sustainable and integrated approach to worm control.

Strategies to minimise worm risk include maintaining late pregnant ewes in condition score 3 to promote good immunity. This nutritional state is also fundamental to encouraging optimum lamb survival. While ewes become more susceptible to worms around lambing time this is negated by low-to-negligible WECs as well as having paddocks prepared with low worm contamination for pre-lambing ewes. In contrast repeatedly relying on chemicals to control worms will inevitably lead to worm resistance and chemical failure.

Another increasingly popular trend is the use of capsules pre-lambing, representing the ultimate reliance on chemicals. It is reputedly popular because of the sustained worm control promoting dag-free lamb growth. Using appropriate monitoring & paddock preparation this strategy is unnecessary and lambs should not be at risk to worm burdens before weaning. The weaning drench is the most important drench in the life of a sheep, but a WormTest can still be conducted pre-weaning to monitor the effectiveness of the pre-lambing worm management.

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