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Rain bodes sheep worm and fly risk

By Colin Trengove, Pro Ag Consulting

Many parts of SA received in excess of 20mm rain in late November / early December which had mixed blessings. Regardless of location it has increased the sheep worm and more immediate flystrike risk for the next few weeks.

The rain may produce an invaluable green pick, plus it may have enabled the sowing of a summer crop in areas that have finished harvest. It will have handicapped those still harvesting and extended the growing season for others.

A common risk for many areas will be Haemonchosis or Barbers pole worm infection. This will normally take 3-5 weeks to emerge and so worm egg counts done in several mobs 3 weeks after 20 plus mm rain can give a good assessment of worm risk.


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.

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. Fortunately, most drench groups are effective against Haemonchus in southern Australia, but some are specific to Haemonchus and have 4-6 weeks benefit.

Always consider Haemonchosis where worm egg counts have risen rapidly to exceed 500 during summer, especially following significant rainfall. A refinement to the traditional worm egg count procedure is a relatively new 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 costs $75+ but the additional information is worth it. This test is only available through certain laboratories and so contact your animal health advisor for details.

A dipstick test detects blood in faeces as another means of diagnosing the presence of Haemoncus infection. This was developed as a race-side diagnostic test more relevant to the Haemonchus-prone summer rainfall regions such as the New England tablelands in NSW. The Haemonchus dipstick test can be purchased through your local rural merchandise retailer.

There is always plenty happening on farms at this time of year and no one needs more distractions. Most people plan to minimise flystrike risk at harvest time, but not many will be thinking about worms. However, given the value of sheep and wool, a few timely worm egg counts now could be money very well spent.

For further information contact your local Livestock Consultant (https://www.salivestockconsultants.com.au/) or veterinarian.