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South Australia worms, flies and lice update - March 2021

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

While flooding rains hit NSW all we have received in the last two months in SA is hollow predictions of rain. These are potentially good worm killing conditions, but the relatively mild summer/autumn temperatures has most likely annulled this eventuality.

As is usually the case at this time of year recent worm egg count (WEC) monitoring indicates elevated worm burdens primarily in mixed age ewes from the higher rainfall areas (>500 mm), with the odd exception suggestive of exceptional worm control or a recent drench. Approximately two-thirds of WECs have indicated a drench is warranted. Potentially the concern with this observation is that elevated WECs in autumn forebodes significant pasture worm larval contamination which will carry over to winter worm burdens. A second summer drench in late January–early February may have circumvented this circumstance. It also alerts to the importance of monitoring WECs six weeks prior to lambing to decide if a drench is required as well as what product to use. If a pre-lambing drench is indicated make sure to use a triple active to optimise the efficacy and minimise the risk of drench resistance. Refugia management should also be included — i.e. leave 20% of the fittest ewes undrenched or drench the entire mob and return them to their current paddock for a week after drenching, before moving to a new paddock. This is to encourage maintenance of a more susceptible population of worms on pastures.

The presence of a short green pick either due to the influence of heavy dews on perennial species or intermittent rain received by some areas increases the risk of developing a worm infestation as sheep graze close to the ground. Monitoring at least alerts to this risk so that strategies can be put in place to prevent escalation of worm burdens in winter. However, the perennial desire to minimise the risk of drench resistance emerging relies on worm control strategies other than use of the drench gun. It is a legitimate criticism that modern farming practices rely too much on the use of chemicals and too little on alternative strategies to maintain productivity and health. Worms are no exception and so keeping ewes in condition score 3 during summer/autumn so that they can maintain their natural immunity to worms and other diseases is paramount to integrated pest management. This may include containment feeding to both reduce their energy requirements by around 20% as well as allowing pastures to recover without worm larvae being deposited (i.e. a double benefit). It is however recommended that ewes are drenched into containment unless they have a negligible worm burden.

Other strategies that should already be in place is preparation of weaning paddocks by minimising worm contamination on these paddocks for the six months in the lead up to weaning. This is primarily achieved by avoiding grazing by wormy sheep. A worm drench is still recommended at weaning as worms can account for up to 60 gm/day reduced growth rate, and so ‘worm-free’ grazing post-weaning is the ideal start in life for a weaner.

More creative integrated pest management measures include establishment of pastures that specifically suppress worm burdens — i.e. those that contain a high condensed tannin content such as sulla, plantain and strawberry clover. Another option is the use of Bioworma supplement to spread nematophagus fungi in the dung that kill worm larvae on the pasture. However, this strategy is restricted to smaller flocks due to the current cost of Bioworma.

A recent discussion with a lamb feedlotter revealed he always anticipates a sheep lice infestation with about one in four mobs of lambs purchased. This is in keeping with estimated lice prevalence in the market place. I mention it as a salient reminder for those who trade sheep that lice as well as worms are an ever present biosecurity risk that you need

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