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When to WormTest and when to drench

WormBoss worm control program

NSW non-seasonal rainfall


When to WormTest and when to drench

Why check worm burdens in sheep?

Checking worm burdens with a WormTest is essential for correct and timely drenching decisions.

The result is healthy sheep, without unnecessary drenching. WormTests are the best basis for drenching decisions. Weight loss, a tail in the mob, pale skin and eyes, bottle-jaw, and deaths may mean that your sheep need drenching. If so, these signs occur well after production losses from worms are already occurring in the mob. WormTests give early warning of significant production losses.

How are worm burdens tested?

Checking worm burdens throughout the year using WormTests is a critical part of the WormBoss worm control program.

WormTest just before sheep are mustered for routine management events. Also, WormTest at 6–8 week intervals after a drench is given or, if a drench was not required, after a suitable period, as shown by the Drench Decision Guide.

Most WormTests are done through a laboratory. However, worm egg counts (but usually not larval cultures) can be done by producers if they have the equipment and skills.

Which mobs and how many should have a WormTest?

WormTest at least one in every three mobs that are similar regarding drenching history, paddock type and class of sheep.

Testing just representative mobs saves the cost of testing all mobs. But this assumes the mobs, their paddocks and drenching history are quite similar. If in doubt, test additional mobs.

When should WormTests and drenches be routinely done?

Routine drenching times

In this region there are 2 times when sheep should be drenched in most years without a prior WormTest.

These are:

  • the ‘first summer drench’

All sheep receive this when pastures are haying off in late spring/early summer). In dry or drought years do a WormTest beforehand as a drench may be unnecessary and could cause increased selection for drench resistance. In the eastern Riverina, this could be delayed until immediately post-harvest and be based on a WormTest.

  • lambs at weaning

This may coincide with the ‘first summer drench’. Weaned lambs are highly susceptible to worms, especially from the stress of weaning. There may also be high worm-risk in wet seasons.

Drenching will help weaners to achieve the growth rates needed for survival. Autumn-drop lambs may also need an additional drench 8 weeks after weaning. For spring-drop lambs, additional drenching after weaning should be done on the basis of WormTest results.

Routine WormTest times

WormTests can be done at any time, however there are certain routine times to WormTest:
(Note: a larval culture (larval differentiation) is useful with all WormTests, and should at least be done occasionally to identify whether barber’s pole worm are common on the property. However, they should particularly be done on properties with a history of barber’s pole worm or otherwise as shown below.)

  • from March till October, 4–6 weeks after significant rain (20+ mm) that has follow-up rain (10+ mm) within a few weeks, including the autumn break
  • young sheep in May/June before the more severe winter weather arrives (may not be required in the drier eastern Riverina)
  • pre-lambing (also include a larval culture if barber’s pole worm have been a problem in the past year) (may not be required in the drier eastern Riverina)
  • prior to other management activities (such as crutching, joining, shearing and weaning) as directed by the Drench Decision Guide

When are other WormTests done and drenches given?

The timing of WormTests and drenches will vary between farms and seasons. Use the Drench Decision Guide (see below) to weigh up important factors when deciding when to drench or WormTest on your property. These factors are signs of worms, time since last drench, the persistence of the last drench, WormTest results, recent rainfall, and condition of sheep and pastures.

If drenching is done for other reasons (such as an early drench before holidays or harvesting), recommence WormTests 6–8 weeks after the drench was given. Then use the Drench Decision Guide to decide when to drench or WormTest again.

Barber’s pole worm in this region is usually sporadic and short-lived. If summer and/or autumn are unusually wet, check worm egg counts each 4–6 weeks through to early winter to identify unusual increases in barber’s pole worms before they cause production loss and deaths. If worm egg counts exceed 1000 epg (or a little lower if sheep are in poor condition), drench with a short-acting drench effective against barber’s pole worm or closantel (generally effective in this region). Test again in 4–5 weeks.

If your property faces a significant barber’s pole worm risk for several months each year seek professional advice regarding an effective program, which may include the Barbervax® vaccine.

What samples should be collected for WormTests?

Sheep do not need to be yarded for a WormTest. Collect fresh dung from the paddock. Obtain WormTest kits or sample collection details from laboratories or resellers in your area. Follow the instructions provided in the kit.

  • Avoid delays in transit (when worm eggs can hatch) by collecting and posting early in the week.
  • Ensure samples are kept cool, but not refrigerated, before sending.

If you do your own worm egg counts, use the ‘bulk’ sampling method where all of the dung is collected into one container.

  • Collect 3 pellets per pile of dung from at least 20 individual piles of fresh dung.
    • Choose pellets of equal size so that each sheep is equally represented.
    • If dung consistency is runny, use a plastic spoon. Don’t avoid runny or soft dung.
    • Collect lamb and ewe samples separately.
  • Dung should be very thoroughly mixed together before preparing your solution for counting.
  • Count 5 chambers from the sample.

See ‘Checking a mob of sheep for worms with a WormTest’.

The WormBoss Drench Decision Guide

The Drench Decision Guide is reliable and helps to simplify decisions. There is a version of the Drench Decision Guide for each WormBoss region.

The guides consider:

  • whether signs of worms are present
  • the class of sheep
  • the WormTest results
  • the condition of the sheep
  • the condition of the pasture
  • the likely worm contamination of the paddock

The Drench Decision Guide will recommend:

  • whether to drench now
  • whether to use a persistent drench
  • when to WormTest again

Results from the Drench Decision Guide can be applied to mobs without a WormTest if other mobs (same class, and similar drenching and paddock histories) have been tested. If in doubt, WormTest the mob.

How to use the Drench Decision Guide

You can use the Drench Decision Guide at any time, whether you are contemplating drenching a mob now or in coming weeks. Not all situations require a WormTest: the Drench Decision Guide will recommend when these should be done.

  1. Firstly, refer to the Drench Decision Guide, which is provided separately.
  2. Start on the page that shows the ‘Drench Decision Guide Questions’.
  3. Read Question 1.
  4. Follow the ‘go to’ information on the right for the answer that applies to your mob.
  5. Only go to the question or recommendation to which you are directed by your answer.
  6. When you are directed to a letter, this is the final recommendation, and is shown on the next ‘Recommendations’ page.
  7. Also read the important information in the green boxes.

See the Drench Decision Guide.