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Home Learn About Sheep Worm Control in Australia Online Learning: Pastoral—Worm Testing

Online Learning: Pastoral—Worm Testing

Aside from drenches at one or two strategic times the mob’s average worm egg count should be the basis for other drenching decisions.

Structured reading

For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the dot point provides a summary of the page.

Tip: Keep this page open and open the links in new tabs.

Checking a mob of sheep for worms with a WormTest
How-to guide to collect and submit samples for a mob worm test to a laboratory.

Worm egg counting
How worm egg counting is carried out.

Assessing worm burdens without a WormTest
Other ways to assess whether sheep have worms and what level of worms exist.

Collecting dung samples from individual sheep (optional)
How-to guide on collecting dung samples from individual sheep (for drench resistance tests or genetic assessment of worm resistance).

Worm testing for ram breeders (optional)
How-to guide for ram breeders who want to gain worm egg count or dag breeding values for individual sheep.

Question and answer

For those who prefer a problem based approach to learning, answer the following questions.
Each of the questions below links further down the page to the answers.


  1. How many individuals should be sampled for a WormTest?
  2. Name a standard time when you should WormTest.
  3. What 2 things does a larval culture tell you and how these help you make a drenching decision?
  4. Name a situation when you would drench without a WormTest?
  5. You can use the WormTest from one mob to make drenching decisions about similar mobs. For every mob you test how many other mobs could this represent?
  6. If only very few sheep (less than 2%) in a mob appear to be badly affected by worms: ? What could be a cause of this? What action would you take?


You can also click on each question below to go to WormBoss pages with related information.

1. How many individuals should be sampled for a WormTest?

Collect the number of samples per mob as recommended by your laboratory (ideally this would be from at least 20 sheep—if you are doing your own worm egg count on farm, try the following ‘bulk collection’ method.

Bulk collection method

  • When conducting your own worm egg counts on farm:
  • Collect three pellets per adult pile (or the equivalent amount if soft or runny) or five for weaners.
  • Collect from at least 20 dung piles.
  • Where Haemonchus (barber’s pole worms) are an issue, and if the mob has over 200 sheep, collect from each of 40 dung piles.
  • Collect all dung into one container
  • The dung then needs to be mixed extremely thoroughly.
  • Conduct your worm egg count using a sub-sample from the bulk mixture.

Read More

2. Name a standard time when you should WormTest.

In this region, drenches should not be routinely given. Always conduct a WormTest before drenching sheep (except when introducing sheep and in unusual cases of predicted extensive flooding, see below). Don’t forget the rams.

Include a larval culture with the WormTest in areas or on properties with a history of barber’s pole worm, or when there is higher than normal summer rainfall, or where animals show signs of anaemia (pale inside eyelids) or bottle jaw (swelling under the jaw).


  • Sheep showing signs that suggest a worm infection
    Scour worms: dark scours (or sometimes clotted dung instead of pellets); weight loss; death.
    Barber’s pole worm: anaemia (pale inside eyelids and gums); ‘bottle jaw’ (swelling under the jaw); lagging or collapse when mustered; death.
    Note: A WormTest can save an unnecessary drench if signs are from another cause, however, if severe anaemia and bottle jaw are noted, an immediate drench for barber’s pole worm is usually warranted. A concurrent WormTest should also be carried out (take samples before drenching) to confirm the diagnosis, as similar signs may occur in this region from the blood parasite Mycoplasma ovis (formerly called Eperythrozoon ovis) and other causes.
  • Prior to weaning lambs
    Lambs are the most susceptible mob on the property: if only one drench is ever needed on a property it will be the weaning drench. If monitoring worm egg counts and productivity over a number of years shows drenching at weaning is not required on your property, only WormTest again at weaning if the conditions have been wetter than usual.
  • Before mustering for management events
    As sheep are mustered infrequently in this region, it is good to conduct a WormTest before mustering for routine activities such as shearing or crutching, rather than drenching ‘just in case’.
  • 6 weeks after rain that has resulted in a green pick of annual grasses and herbage
    Generally, a single fall of rain won’t cause a significant increase in worms in this region. However, follow up rain sufficient to allow annual grasses to germinate and persist will also favour development of worm larvae; sometimes these can increase to a serious infection within a month or two.
  • 4–6 weeks after sheep have been congregating in small areas
    When sheep are restricted to smaller areas, such as when paddocks are flooded, they are forced to re-graze areas more quickly and heavier than normal. The pasture becomes more contaminated with worm eggs and if conditions have favoured egg hatching, the sheep will have higher worm infections.
  • Each 2–3 months for sheep on bore drains/irrigation channels when there is little other paddock feed
    In very dry times or drought (when worms are otherwise not expected), sheep preferentially graze green pick along drains and channels. This can lead to higher levels of worm contamination along the drains, and infection and illness in the sheep, compounded by the generally poorer condition of the sheep in these times.
  • November/December and February in north-west Victoria and the western Riverina
    In years when winter and spring have been much wetter than usual check whether a first summer drench (November/December) and/or second summer drench (February) could be required. Under these conditions consider a WormTest when the pasture is haying off and again in February.
  • In southern Queensland, if autumn and winter were wet and the spring and summer is wet or likely to be wet, WormTest each 4–8 weeks (depending on the amount of rainfall) until the season dries out.

Read More

3. What 2 things does a larval culture tell you and how these help you make a drenching decision?

A WormTest refers to a ‘Worm Egg Count Test’ or ‘WEC test’; it will identify the number of worm eggs in faeces, which is a good indication of the worm burden of the sheep.

Some laboratories can also perform a ‘Larval Culture’ (also called a ‘Larval Differentiation’) to identify the types of worms present and their proportion (the importance of this varies according to your location).

Read More

4. Name a situation when you would drench without a WormTest?

  1. When giving a quarantine drench.
  2. When giving a strategic drench. The timing of strategic drenches depends on the region and the class of sheep, as their use is closely associated with times when sheep are most susceptible to worms or when development of eggs to infective larvae on pasture is likely to be extremely low (to reduce pasture contamination) or high (to pre-empt likely immediate problems). Strategic drenches are given regardless of the average worm egg count of the mob.

There are six common strategic drenches; not all are used in every region. The WormBoss programs outline which strategic drenches to use in each region.

  • Pre-lambing ewes
  • Lambs being weaned
  • Winter weaners going into low worm-risk paddocks
  • Smart grazing
  • Summer drenches—temperate winter rainfall regions
  • Summer-autumn drenches—Mediterranean climatic regions

Details of when/how to use strategic drenches are in Your Program.

Read More: Drench Decision Guide for this region

5. You can use the WormTest from one mob to make drenching decisions about similar mobs. For every mob you test how many other mobs could this represent?

Ideally each mob should be tested individually, as there are usually differences between paddocks in the favourability for worm survival, the number of worm eggs being deposited by different mobs, and the time since a drench was given. However, if there are a number of mobs that have the same drenching history, same class of sheep and very similar paddock type (including recent level of contamination from worms) then one mob can represent two others (i.e. test one in every three similar mobs).

Testing representative mobs saves the cost of testing all mobs, but carries the risk that the result may not be representative.  If in doubt, test additional mobs. Testing individual mobs is suggested for Western Australia, South Australia, Victoria and Tasmania.

Read More

6. If only very few sheep (less than 2%) in a mob appear to be badly affected by worms: ? What could be a cause of this? What action would you take?

If less than 2% of a mob are showing signs that include pale inside eyelids and gums, bottle jaw, lagging or collapse, you should treat these affected sheep immediately with a drench suitable for barber’s pole worm, but also sample and test the remainder of the mob now. If these signs are not visible, but a few sheep are scouring badly, test the mob now. In both cases, use the results with your Drench Decision Guide to decide whether the whole mob should be treated.

When less than 2% of a mob show signs of worms these are the possible causes:

  • These sheep were not drenched when the rest of the mob were (e.g. didn’t get mustered, were missed or spat out the drench in the race, strayed in from another mob). Their worm egg count may be a lot higher than the rest of the mob.
  • These sheep are suffering from some other illness or injury that has reduced their immunity and they have acquired a larger worm burden than the rest of the mob. Signs of another problem may be evident.
  • These sheep are the most susceptible in the mob because of lower worm-resistance and the mob has been tested just when these first sheep are starting to show signs.
  • These sheep are not actually affected by worms at all. Instead, anaemia could be the result of liver fluke and scouring could be from larval hypersensitivity, coccidiosis or excess lush feed.

In all of the above situations, a WormTest on the remainder of the mob (don’t include these badly affected sheep) to determine the worm egg count will inform your decision of whether to treat the rest of the mob.

Drench Decision Guide – Pastoral

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