Back to State Outlooks

South Australia worms, flies and lice update - June 2021

SA WormBoss Worm Control Programs

SA WormBoss Drench Decision Guides





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

Season opening rainfall finally prevailed by mid-June for most agricultural areas in SA enabling seeding to proceed and dry sown seed to germinate. The exception is the higher rainfall areas on the Fleurieu peninsula, KI & SE which had already received handy autumn rainfall.

Prior to the opening rain the combination of very dry soil and scant ground cover has not been conducive to worm larvae survival. Recent WECs reflect this with only carry-over lambs with counts high enough to warrant a drench. This finding most likely also reflects that producers don’t tend to monitor worms prior to lambing and prefer to drench anyway. In addition, the prolonged dry spell has meant that many flocks have been confinement fed potentially enabling better worm control. Apart from preserving ground cover and allowing establishment of newly germinated pasture, confinement feeding has the added benefit of reducing worm larval burdens on paddocks going into winter.

As lambing progresses around the state, it is a good time to start planning both DRTs and paddocks for lamb weaning. DRT is ideally done on lambs around the time of weaning when they’ve had sufficient opportunity to develop a worm burden. Prior to this it is unlikely that lambs have acquired a significant 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 DRT will be most reliable when lambs have not previously been exposed to a drench chemical and have a WEC exceeding 250 EPG. Consult or your animal health advisor for more details.

An ideal pasture for weaning is one that has sufficient good quality feed (at least 1200kg dry matter per hectare or a dense green pasture with an average pasture height of 4cm) to support weaner growth as well as a low worm risk i.e. has not been grazed for four to six 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 six to ten weeks to accumulate 1200kg DM/Ha green feed from the season break and so it is important to be planning the weaner paddocks from autumn. This is far preferable to relying on chemicals to control worms as we all know from experience that chemicals alone are at best a stop-gap measure.

Scouring is often a feature of mid-winter, but don’t assume worms cause them. Worm burdens tend to steadily increase in lambs and kids and can be in the thousands before scouring will become apparent. Conversely, adults will often scour due to worm challenge without having significant worm burdens. This is due to their immune response to worm larvae intake causing bowel irritation and rapid feed throughput.

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 advised before attempting treatment. Well over 100 lambs were lost on one south east property last month due to bacterial scours. 20 dung samples at random are best to assess the level of worm or Coccidial burden while three to five scour samples for microscopic exam and bacterial culture is desirable to diagnose the cause of bacterial scours. 10 blood or liver samples to assess trace element status can also be beneficial in late winter spring if illthrift is also evident.

Lice populations generally increase steadily over winter and so if sheep are yarded it is also a good opportunity to part the wool at least 10 times on 20 sheep to check for their presence. This can be useful forward planning to coincide treatment, if necessary, with a spring shearing.

For June 2021 state outlooks, please follow the links below:
Back to State Outlooks