When to Drench and When to WormTest for Sheep – South Australian 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 before there are 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?

In this South Australian winter rainfall region all mobs should be WormTested separately, rather than using one mob to represent another. Paddock differences here will have a significant effect on resulting worm burdens, even if the sheep are a similar class.

When should WormTests and drenches be routinely done?

Routine drench times

Note: Long-acting drenches are rarely required in South Australia. Unless professionally advised, use an effective short-acting drench when treating for worms. Where treatment for barber’s pole worm is also required, broad spectrum drenches are generally effective as drench resistance in barber’s pole worm is as yet uncommon in South Australia. However, this may be changing in areas where sheep have been introduced from interstate, locations where barber’s pole worm is more common.

South-East

• Lambs at weaning.
• Working rams pre-joining
• The ‘summer drench’ (Late November/December, 2–3 weeks after the feed has dried, but before Christmas)

Higher Rainfall Mediterranean

• Lambs at weaning.
• Working rams pre-joining
• There are no routine drenches for breeding ewes in this zone.

Lower Rainfall Mediterranean

• Working rams pre-joining
• There are no other routine drenches in this zone

Routine WormTest times

WormTests can be done at any time; however there are certain routine times to WormTest, shown below. Use the results with the Drench Decision Guide to decide whether to drench and when other WormTests should be done.

A larval culture (larval differentiation) with the WormTest is particularly useful in areas or seasons in which summer rainfall occurs and barber’s pole worm is a risk.
Note: Ram breeders should be aware that young rams under 2 years are highly susceptible to worms and should be regularly monitored as per weaners.

WormTest in the following situations:

South-East

• Lambs kept on their mothers longer than 12–14 weeks (usually until turnoff)
  Test at 12 weeks then each 4 weeks until turnoff
• Weaners
  Test 4 weeks after the weaning drench then each 4–6 weeks until the end of their second (hogget) winter
• Ewes
  • Pre-lambing
  • Pre-marking
  • Pre-weaning
  • 6–8 wks after marking if weaning is later than 14 weeks
  • 6–8 wks after the ‘summer drench’, then 8 weekly till pre-lambing

Higher Rainfall Mediterranean

• Lambs kept on their mothers longer than 12–14 weeks (usually until turnoff)
  Test at 12 weeks then each 4 weeks until turnoff
• Weaners
  Test 4 weeks after the weaning drench then each 4–6 weeks until the end of their second (hogget) winter
• Ewes
  • Pre-lambing
  • Pre-marking
  • Pre-weaning
  • 6–8 wks after marking if weaning is later than 14 weeks
  • 8 weekly from when the feed is drying until pre-lambing

Lower Rainfall Mediterranean

• Lambs at weaning
  Many lamb mobs do not require drenching. Your options are:
  • Test prior to weaning by collecting only lamb dung (lamb dung is a smaller size—do not collect ewe dung as ewes can often have extremely low counts while lambs can have higher counts.)
  • Test at weaning after lambs are separated: collect dung and keep lambs nearby until results are received.
  • (Or drench all lambs at weaning, but this is not the preferred option as many mobs will not need drenching)
• Weaners
  • Test 6 weeks afer the weaning drench
  • Thereafter test at intervals depending on their feed quality: green pasture (6 weekly), dry pasture (8 weekly), on crop stubbles (10 weekly), until the end of their second (hogget) winter.
• Ewes
  • Pre-lambing
  • Weaning – test ewes if more than 10% are scouring
  • Just before harvest
  • 10 weeks after the pre-harvest test (if on pasture) or when ewes leave crop stubble

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, WormTest results, time of the year, 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.

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).

To conduct a WormTest obtain sandwich bags (not ziplock) for individual animal samples and then follow the instructions provided by your testing laboratory or advisor. 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 (refrigerate but do not freeze) before sending, include an ice brick in transit in very hot weather and exclude as much air from the sample bags as possible.

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.

See ‘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

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.

The printable and an online interactive version of the region’s Drench Decision Guide are available here: