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South Australia worms, flies and lice update - July 2019

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Modest rainfall across most of the State has been welcome, but lack of soil moisture reserves means that it is vital that the pattern continues or improves. As expected, the higher rainfall areas have received more rainfall since April, and worm egg counts tend to reflect this.

Worm egg counts have generally been below the 200 eggs per gram threshold across age groups and most of the State in recent weeks except for the southern Eyre Peninsula and the South East where counts have exceeded 1,000 eggs per gram in both lambs and ewes. This variability highlights the need to monitor worm counts in lambs and ewes as restricted feed availability will limit lactation and encourage lambs to graze more, leading to increased worm larvae pickup. Similarly, the longer the access to short green feed through winter, the greater the risk of increasing worm burdens.

High egg counts in lambs provide ideal circumstances for doing drench resistance trials. Keep this in mind before planning to drench lambs at weaning as drench resistance is ideally monitored with DrenchTest at least every three years. Check the process with your animal health advisor if you are not familiar with the procedure.


Scouring is often a feature of grazing lush green feed during winter, but don’t always assume worms are the cause. Worm burdens tend to steadily increase in lambs and kids and can be in the 1,000s before scouring is noticed. Conversely, adults will often scour despite a low egg count, and this can be due to worm challenge or simply the excess fluid and lack of fibre in the diet. Worm larvae can also stimulate an immune response in adult sheep causing more rapid feed throughput (scours or diarrhoea) including the worms which haven’t had a chance to develop into egg-laying adults.

Several bacteria (Campylobacter, Yersinia, Salmonella), as well as a protozoan parasite (Coccidia), are recognised as potential causes of scours in lambs and kids, and so a correct diagnosis is critical to choosing the best treatment. Twenty dung samples collected at random are best to assess the level of worm and/or Coccidial burden while 3–5 scour samples for microscopic examination and bacterial culture are desirable to diagnose the cause of bacterial scours. Ten blood or liver samples to assess trace element status can also be diagnostic in late winter/spring where scours and/or ill thrift is evident.

Lice populations generally increase steadily over winter and if sheep are yarded, it is also a good opportunity to part the wool at least ten times on twenty sheep to check for their presence. This may also be useful for forward planning to coincide treatment with a spring shearing.



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