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Best Practice

Production Loss

Drenching Sheep

Why am I drenching?

Sheep Internal Parasites & Best Practice Worm Monitoring

Key principals of drenching:

Avoid unnecessary drenching

Calibrate all drench guns to ensure the correct dose is given

Calculate the dose rate based on the heaviest animals in the mob (if there is a significant weight range, split the mob)

Follow all drench label instructions

After drenching, graze the animals initially on the already contaminated paddocks. As the eggs left after drenching will be diluted by the larvae already in the paddock.

Knowing when to drench

Traditional Internal Parasite High Risk Seasons2

Traditional Internal Parasite High Risk Seasons

This graph shows time periods of increased larval pasture survivability - individual areas and different seasonal conditions can influence these high risk periods

Drenching Ewes before Lambing

Because of the Peripaturient Relaxation of Resistance, ewes carry more worms and these worms all lay more eggs, leading to loss of ewe condition, less milk production and contamination of lambing paddocks. To avoid this, ewes should be monitored for FEC, and consider drenching approximately 2-4 weeks before the planned start of lambing.  Long-acting drenches may be useful during this period if pastures are highly contaminated.

After weaning, ewes should be monitored by FECs.  Any loss of body condition score (BCS) should be made up while pasture supplies are plentiful, as it is more expensive to fatten ewes on supplements than on grass.

The diagnostic tools

Treating lambs at marking is often done but can rarely be justified, as at the age of marking (2-10 weeks old) lambs usually aren’t carrying a significant worm burden.

It is better to monitor the FEC of lambs before and immediately after weaning, to check when a drench is required. If a short acting drench is used, continue to monitor FECs 2 weeks later to check efficacy, or 1 month later to see when the next drench is needed.

FEC pack


When choosing a drench you need to know:

The specific properties and potential uses of all of the different drench groups 

The current drench resistance status of the drench group on your property

Drenches are often classified on the basis of their range of activity and/or the class or type of active ingredient(s) that they contain.

Broad-spectrum drenches provide activity against most of the important worms of sheep, provided they are susceptible to the drench.

Narrow-spectrum drenches generally just have activity against one or two species of sheep worms.  It is preferable to use these against specific worms (e.g. an infestation of Barbers Pole Worm) rather than a broad-spectrum drench.
Long-acting treatments (injections or boluses) are useful treatment options when stock are in contaminated pastures. However, they can lead to rapid onset of resistance if misused.
A combination drench contains two or more active ingredients that each targets the same worms. This gives an increased chance that worms resistant to one active are killed by the other active. This can be useful as many farms have worms resistant to more than one active (Wormboss).


No clean paddocks are available i.e. those with minimal worm burdens.

With pre-lambing ewes towards the end of pregnancy to avoid handling.
  • interventions need to be limited to avoid stress and not closer than 2 weeks to lambing
  • reduced handling will lower the risk of pregnancy toxaemia in late pre-lambing ewes and mis-mothering if lambs are already on the ground.

If long-acting drenches are being used, it is vital they are used responsibly.

Note: Capsules play a very similar role to LA drenches and they should also be used responsibly.


The irresponsible use of LA products may render that class of actives ineffective on that property.  This means that not only the moxidectin in Sheepguard LA will be at risk, but also the other MLs.

With a longer protection period expected, an ineffective drench can result in:
  • dead sheep
  • lost productivity
  • no value for money
  • sheep seeding paddocks with resistant worms.
Accelerated drench resistance emerging due to sub-lethal levels of the LA active in the sheep


1.  Priming drench (given at the same time as the long-acting product):

use an effective short-acting drench, preferably a combination, which includes an active from adif ferent class (group) to the long-acting product
it clears the sheep of any worms including those that are resistant to the long-acting drench.

Startect® with its new class of active in combination is an effective priming drench.

Startect is the only drench to contain a Spiroindole class (SI) of active in Derquantel making it a good priming partner with LA drenches.

2.  Pooled worm egg count tests at the 30, 60 & 90 day mark following the LA treatment:

testing at these times will give an accurate measure of the efficacy of the program in use
any eggs indicate the end of the long-acting pay-out period and the need to schedule the tail-cutter drench
gives greater certainty as to when the treatment is becoming ineffective.

3.  Tail-cutter or exit drench is used two weeks after the end of the actual protection period:

use an effective short-acting treatment, preferably a combination, which is from a different class to the long-acting product
ideally done 2 weeks after the long-acting protection period expires
kills larvae that have survived the persistent treatment and developed into breeding adult worms.


Responsible use will result in

Greater productivity, increased sustainability and overall better value-for-money
A longer and more sustainable use of the more fragile single active ML (mectin) drenches
Opportunities to add value by informing and promoting best practice
Being able to continue using LA treatments into the future.

Sheepguard Long Acting Injector Instructional Video

Further Reading

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