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South Australia worms, flies and lice update - December 2020

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

The weather has followed a vague pattern in recent weeks with alternating brief hot spells of 1–3 days, followed by a similar cool period interspersed with occasional showers. This has made for good living conditions but a little temperamental for harvesting and no doubt well suited to worm survival. As can be expected there have been reports of Haemonchus or barber’s pole worm causing sheep losses, and this will be a recurring issue while this weather pattern persists.

Isolated showers through spring and now into December in parts of the State have set up ideal conditions for Haemonchus and flystrike. Both could easily catch sheep producers off-guard when treatment products may be hard to come by (e.g. during Christmas/New Year). Drenching at this time of year needs to be broad-spectrum, but repeated rainfall events may warrant the inclusion of the chemical closantel to provide 4–6 weeks sustained action against Haemonchus. There are few ‘multi-active’ products that include closantel, so these may need to be ordered in at a time when supplies are limited. In addition, monitoring worm burdens can also be problematic through the holiday period.

The unique characteristic of Haemonchus is that it relies on blood sucking for survival and has the capacity for rapid population explosion. Scouring is not a feature, but lethargy and ‘bottlejaw’ (i.e. submandibular oedema) is; these are signs that need to be closely monitored. In as little as three weeks following 20+ mm rain it can be killing sheep of any age due to anaemia. It prefers warm moist conditions and so is renowned for causing stock losses in or after wet summers — especially in paddocks with soakage areas and sandy soils that retain moisture.

It is worthwhile checking the colour of the conjunctiva or gums of sheep showing lethargy or sudden death without scouring at this time of year. Pale or white gums is almost diagnostic for Haemonchus and indicates urgent action is required. Just the stress of yarding anaemic sheep can be sufficient to kill them, and so early diagnosis and treatment is critical. Refer to specific information on the WormBoss website for more detail. If a sheep goes down during the muster and has pale gums, leave it, then go back and drench it in the paddock; trying to get them to the yards, even on the back of the ute or bike, can often result in their death.

Worm egg count (WEC) monitoring results in recent weeks have been quite variable, which is reflective of the good spring combined with intermittent rainfall and a range of monitoring and drenching strategies. Always consider Haemonchosis where worm egg counts have risen rapidly to exceed 500 eggs per gram during summer. A refinement to the traditional WEC procedure is the faecal qPCR test that checks for worm DNA in faecal samples, allowing the number of Haemonchus and other roundworm species present to be quantified. It takes about 3–4 days to get a result and costs $75+ but the additional information is worth it. This test is only available through certain laboratories, so contact your animal health advisor for details.

The year has finished well season-wise for most producers, but the sheep population remains limited due to the sustained high market price for sale lamb and mutton. Unfortunately, we cannot say the same for wool, but hopefully that will bounce back with a correction in trade with China in 2021. The value of sheep further heightens the need to monitor their health closely so that the new year can bring new prosperity. I wish you all a happy festive season & new year.

For December 2020 state outlooks, please follow the links below:
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