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South Australia worms, flies and lice update - June 2019

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Rain in May achieved germination followed by another 30 mm in early June that “saved the day” for most agricultural areas after the driest six months in over 50 years. Green feed is still short, but at least alleviates the need for very expensive and almost non-existent hay and grain supplements. Lack of ground cover may cause a fibre shortage in the short term, but confinement feeding across the state will hopefully have preserved some dry residue in paddocks.

Prior to June, the combination of dry soil and scant ground cover has not been conducive to worm larvae survival. Recent egg counts reflect this with only lambs and lactating ewes exceeding 200 eggs per gram. However, be mindful that this finding is likely to be biased as producers that do monitoring, are more likely to manage worm burdens better, including the strategic use of anthelmintics. In addition, confinement-fed flocks may have had better worm control if they were drenched upon entry to the confinement area. Apart from preserving ground cover and allowing the establishment of newly germinated pasture, confinement feeding has the added benefit of reducing worm larval burdens on paddocks.

As lambing/lamb marking continues around the state, it is an excellent 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. Before this, it is unlikely that lambs have acquired a significant worm burden, and so drenching at lamb marking is not 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 on how to get reliable results from this procedure.

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 height of 4 cm) to support weaner growth, as well as a low worm risk, i.e., has not been grazed by sheep for 4–6 months. A previous long dry summer/autumn facilitates a reduction in worm risk provided a paddock has not been grazed during this period. It usually takes 4–6 weeks to accumulate 1200 kg DM/Ha green feed from the season “break” depending on soil temperature and fertility. Planning the weaner paddocks ideally begins at the start of summer to minimise worm risk as well as allowing sufficient time for pasture growth.

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