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55 Victoria Road
Clare SA 5453
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Ph  08 88422822

Consulting Hours:
Monday to Friday


4 Vohr Street
Jamestown SA 5491
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Ph  1300 CV VETS (1300 288 387)  Ext 2

Consulting Hours
Tuesday and Thursday

  Clare Clinic

Clare Valley Veterinary Services
1300 CV VETS (1300 288 387)

Clare  Ext 1 Jamestown Ext 2     Balaklava Ext 3
  Monitoring Worm Burdens in Sheep Flocks


The folllowing article is courtesy of Dr NIgel Baum BSc BVMS ( Hons) Veterinary Officec



Worms cost Australian sheep producers more than any other animal health problem.

In order to have a successful sheep enterprise, it is essential that producers are able to control and manage this animal health issue.

The good spring in 2010 followed by the wet summer provided perfect conditions for the survival and persistence of high levels of sheep worms on paddocks. There were many cases of production loss, scouring and deaths in sheep flocks due to worms last year, and the risk of worms is even greater this spring.

In recent months a number of cases of sudden death, production loss and scouring in sheep across the region have been submitted to the PIRSA Disease Surveillance Scheme. Testing showed the sheep have had large worm burdens.

Having faecal worm egg counts done on a sample of faeces from your sheep is strongly advised this spring & summer – especially the lambs/weaners. This will give you information on what worm burden your sheep are carrying, and whether drenching is required BEFORE you have a major problem. You can also use the same procedure to check if your drench has worked.

The significance of the number of worm eggs in the faeces depends of the type of worms involved, the class of sheep, and the grazing system used. This is why getting professional veterinary advice to interpret the results is vital, allowing you to develop a comprehensive worm management plan.

Methods used to control worms can involve non-drenching and drenching options.

Some non-drenching options include the following:

q       Cross grazing with cattle. Alternative grazing between sheep and cattle is effective as most worms infect only sheep or cattle. Grazing a paddock with cattle for 6 months will reduce the number of sheep worm larvae enormously.

q       Nutrition. Sheep that are in a good nutritional state will not be affected by worms as much as sheep that are in poor condition or under stress. This is due to the fact that an animal in good condition has a strong immune response to larvae when they are eaten from the pasture.

q       Fodder crops and crop stubbles. Cropped paddocks have very low levels of worm contamination. This applies to paddocks sown for grain as well as hay & silage.

q       Worm Resistant Sheep: It has been demonstrated that selecting for worm resistant sheep results in animals with lower worm burdens. For most commercial sheep producers the way to incorporate this technique into your management is to purchase rams where selection has occurred for this trait. Some stud producers consider this in their selection criteria.

q       Rotational and Cell Grazing. This is sometimes considered a valuable tool in reducing the number of worm larvae on the pasture. However, in many cases, the intervals between grazings are not long enough to reduce the pasture worm contamination levels.


When controlling worms with drench, it is important that the drench is used effectively. Drenching effectively involves:

q       Using the right drench that is effective on the worm population in the flock ie using drenches with little or no resistance

q       Using it at the right time

q       Using it at the correct dose rate

q       Administering it to the animal in the correct way


Drench resistance is a major issue in the Australian sheep flock. Knowing which drenches are effective on your property is essential to choosing the right drench for your flock. The number of farms in Australia with resistance to the white and clear drenches is greater than 90 % and 80 % respectively. Resistance to ivermectin drenches ranges from 30 -80 % depending on location in Australia. A new drench (monepantel) has recently been released and has no resistance. It is very important that this drench is used carefully to ensure that resistance does not build up.

The way to measure drench resistance in your flock is to do a faecal egg count reduction test. You should contact your private veterinarian for advice on undertaking this test. The information gained from this test is critical to having a well managed worm control program.

Drenches need to be given at the correct dose rate – check the label directions. Under dosing is one factor in increasing drench resistance in a flock. Drench guns need to be regularly checked to ensure that the correct dose is being given.

For white and ivermectin drenches, the efficiency of the drench can be improved by holding the animals off feed for 12 -24 hours. This should not be done for clear, OP or Closantel drenches as this can increase the risk of toxicity.

For more information on sheep worm control, contact Clare or Jamestown Vet clinic, your local PIRSA Animal Health office or visit the WormBoss web site at




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To contact any of our clinics please phone:

1300 CV VETS (1300 288 387)

Clare Clinic Extension 1

Jamestown Clinic Extension 2

Balaklava Clinic Extension 3


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