Rain Forebodes Sheep Worm Risk

Sheep worms will be revelling as much of SA received more than 30mm rain during mid-November and follow up falls continue. Regardless of location it has markedly increased the sheep worm risk for December.

The rain has provided invaluable summer feed for graziers, but the double-edged sword is torment to devastation for croppers.

A common risk now for many areas will be sheep deaths due to Haemonchosis or Barbers pole worm. This will normally take 3-5 weeks to emerge and so worm egg counts (WECs) done in several mobs 3 weeks after 20+ mm rain can provide a good assessment of worm risk. Similarly, the more common winter scour worms will also be on the rise and so WECs are a valuable management tool to assess the need for a drench.

Haemonchus is unique worm being a blood sucking parasite with a capacity for rapid population explosion. In as little as 3 weeks from emergence 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 wet summers – especially in paddocks with soakage areas and sandy soils that retain moisture.

Another tool is to look for bottle jaw and check the colour of the conjunctiva and gums of sheep showing lethargy or sudden death. Pale or white gums is almost diagnostic for Haemonchus and indicates urgent action is required. Fortunately, most drench groups are effective against Haemonchus in southern Australia, but it is always recommended to use a combination of 3 or more chemicals to optimise worm kill.

Always consider Haemonchosis where worm egg counts have risen rapidly to exceed 500 during summer, especially following significant rainfall. However, a count more than 100 is sufficient to warrant a drench in early summer. Note, a WEC should include at least 15 fresh individual faecal samples submitted to the lab to ensure a reliable indication of worm risk.

There is always plenty happening on farms at this time of year, and no one needs more distractions. Most sheep owners plan to minimise flystrike risk going into summer, but may not be concerned about worms and so a WEC in a few mobs now could be money very well spent.

For further information contact your local Livestock Consultant ( or veterinarian.

Article written by Colin Trengove, Pro Ag Consulting 

November 2021