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South Australia worms, flies and lice update - June 2015

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides

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

The inverse weather pattern in SA this year has resulted in a relative abundance of feed in the top two thirds of the state as well as the lower south east. This appears to have kept worm infestations at a low level due to sheep being in good condition going into the traditional feed shortage period of May/June.

Worm egg counting has been less frequent; perhaps indicative of a lower concern about worm burdens. The few that have been done indicate a low level of worm burdens and no need for drenching. Inevitably, many/most ewes will have been drenched in the lead up to lambing despite the low WECs and abundance of feed as producers tend to be risk adverse at this time. Fortunately, the risk of developing drench resistance at this time is also low as more worms are likely to be surviving on the pasture than in the gut.

The next consideration is the weaning drench. Rarely are lambs in the situation that a drench earlier than weaning is either necessary or indicated. While the weaning drench is usually the most important drench in the life of a sheep it is still valuable information to assess the worm burden in the lead up to weaning. Regular worm egg counting in conjunction with condition scoring and pasture availability and quality assessment provides useful information to monitor worm risk both currently and in future.

Where drenching is indicated, a short acting effective drench is usually all that is required. This can either be one of the new drench alternatives or a combination of the various other chemical actives available. A follow up WEC 10 days after drenching is useful to check the effectiveness of the drench used.

There is a tendency by some producers to use long acting drench options prior to lambing. However, keeping ewes in good condition (i.e. score 2.7–3.3) is a far more beneficial strategy than relying on chemical activity to limit the impact of worms. Ewes in good condition are able to suppress the development of worm burdens as well as encouraging better lamb survival. It also further reduces the risk of drench resistance developing.

An abundance of feed during winter will often result in scouring due to the composition of the feed. This includes high nitrogen and potassium as well as a lack of fibre. Providing ad lib pasture hay or barley straw can counter this development as well as the provision of mineral supplements. However, a persistent scour should be checked for all possible causes such as worms, trace element deficiencies or bacteria such as Yersinia or Campylobacter.

Happy monitoring!

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