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South Australia worms, flies and lice update - June 2018

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Season opening rainfall finally prevailed in June for most agricultural areas in South Australia. More rain is required, but at least seeding got underway and dry-sown seed managed to germinate.

Prior to the opening rain, the combination of dry soil and scant ground cover was not conducive to worm larvae survival. Recent egg counts reflect this with few results indicating a need for a drench regardless of class of sheep. This finding may also indicate that producers that do monitoring are more likely to manage worm burdens better, including the strategic use of anthelmintic. In addition, the prolonged dry spell has meant that many flocks have been confinement-fed. Apart from preserving ground cover and allowing establishment of newly germinated pasture, confinement feeding has the added benefit of reducing worm larval burdens.  

As lambing progresses around the state it is a good time to start planning both drench resistance testing and paddocks for lamb weaning. Drench resistance testing is ideally done on lambs around the time of weaning, when they’ve had sufficient opportunity to develop a worm burden that requires drenching. Prior to this it is unlikely that lambs have acquired a high enough worm burden and so drenching at lamb marking is not routinely recommended. In exceptional circumstances, where lambs have been grazing from day one, a drench prior to weaning may be indicated, but monitoring their worm burden first will clarify this.

A drench resistance test will be most reliable if lambs have not previously been exposed to a drench chemical and have a worm egg count exceeding 250 eggs per gram of faeces. Consult or your animal health advisor for more details.

An ideal pasture for weaning is one that has sufficient good quality feed (at least 1200 kg dry matter (DM) per hectare (Ha) or a dense green pasture with an average pasture height of 4 cm) to support weaner growth as well as a low worm-risk i.e. has not been grazed for 4­–6 months. A long dry summer/autumn facilitates a reduction in worm risk provided a paddock has not been continuously grazed during this period. It would normally take 6–10 weeks to accumulate 1200 kg DM/Ha green feed from the season break and so it is important to be planning the weaner paddocks now.

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