When to Drench and When to WormTest for Sheep – Victorian Winter Rainfall Region

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, scouring, a tail in the mob and deaths may mean that your sheep need drenching. If so, these signs occur well after substantial production losses (reduced weight gain and wool growth) from worms have already occurred 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.

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. Ideally, producers should have their preparation and counting technique reviewed by an accredited laboratory and perform ongoing quality control checks, just like an accredited laboratory to ensure their results are correct.

Which mobs and how many should have a WormTest?

Testing all mobs is the ideal, especially prior to the second summer drench. To reduce the cost of testing you can WormTest at least one in every three mobs with a similar drenching history, paddock type and class of sheep. However, this approach does carry more risk that some mobs that aren’t monitored will have a high count.

If in doubt about how representative one mob is of another, test the other mob.

When should WormTests and drenches be routinely done?

Routine drench times

In this region there are 2 situations where sheep should be drenched in most years, these are

• The ‘first summer drench’ (November/December). All sheep mobs should be given an effective drench in most Victorian regions in November. Don’t forget the rams. If in doubt about the need for a first summer drench in November, consult your vet.

• Lambs at weaning. All lambs should be drenched at weaning. In spring-lambing mobs this usually coincides with the ‘first summer drench’. Weaned lambs are highly susceptible to worms and there is usually a higher worm-risk in wet seasons. Drenching will help weaners to achieve the minimum growth rates needed for survival (at least 1–2 kg/month during the summer and autumn). Use a drench shown to be effective on your property.

Note: The second summer drench (in January/February) is not routinely needed in some areas or in all years. However, it is very important because contamination with worm eggs in late summer and autumn is a strong determinant of the peak availability of worm larvae the following winter (hence worm problems will occur if it is not given); conduct a WormTest to decide whether a second summer drench is needed.

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 particularly useful in areas or seasons in which summer rainfall occurs and when re-infection with scour worms or barber’s pole worm might occur.

• WormTest weaners no more than 5-6 weeks after their first summer drench, especially in wet summers. This is usually the weaning drench for spring-drop lambs; for lambs born in autumn (often early May) WormTest 4–5 weeks after their weaning drench.
• During January–February for sheep showing signs of barber’s pole worm (anaemia and lethargy)—aside from known barber’s pole worm areas this can also occur in wet summers or irrigation areas.
• All mobs in late January/early February, just prior to a possible second summer drench. This will usually be 6–8 weeks after the first summer drench.
• Weaners, 4–6 weeks after the autumn break and thereafter through winter. However under high risk conditions (pastures highly contaminated with worms/higher rainfall areas/wetter than normal) test as soon as 2 weeks after the break.
• 4–6 weeks after any short-acting drench.
• Higher risk mobs in July/August (usually youngest and oldest). Test other mobs if high worm egg counts are found. These results will give a check on peak winter egg counts.
• Ewes pre-lambing (provided it is at least 8 weeks post-autumn break for adults and 6 weeks for maidens). This is especially important for ewe mobs that are struggling with low condition score (less than 2.5) and/or grazing pastures of less than 1200kg DM/ha (3–4 cm pasture height).
• As suggested 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 include 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), 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 warm fresh dung from the paddock (but make sure that ewe and lamb samples are not mixed).

WormTest kits can be obtained from laboratories or resellers in your area. Follow the instructions provided in the kit or talk to an adviser on the best method to use. As a guide, collect 20 individual samples from mobs up to 400 sheep, and 20–40 samples from larger mobs. The laboratory will then ‘bulk’ these samples using an identical amount of dung from each sample.

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

If you do your own worm egg counts, a ‘bulk’ test is easier than counting individual samples. Fewer bags or trays are needed and more sheep in the mob can be sampled.

The following fact sheet is on the WormBoss website: ‘Checking a mob of sheep for worms with a WormTest’.

The WormBoss Drench Decision Guide

The Drench Decision Guide helps to simplify decisions on whether and when to drench. There is a version of the Drench Decision Guide for each WormBoss region. It considers

• 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 providing they are the same class, and have the same drenching and paddock histories. 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.

Each Drench Decision Guide is available as a separate 2-page printable version, or can be used directly online.

Using the print version:

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

Using the web version:

1. Agree to the terms of use and press ‘Start’
2. Select an answer for the first question and you will automatically be taken to the next appropriate question.
3. Select an answer for each question and you will automatically be taken to the Recommendation, where your choices and Recommended Actions will be shown, as well as other important information.

The region’s Drench Decision Guide is available at the link below: