Drenching is currently an important component of a worm control program.

Effective drenching means using:

• the right drench (one that a drench resistance test has shown to be effective against the target worms at the time),
• at the right time (given the recommended local worm management program and current worm egg count monitoring results),
• at the right dose rate and
• administered to the animal in the correct way.

Also see:

• When to drench
• Choosing a drench
• Drenching technique
• Holding sheep off feed prior to treatment
• Holding sheep in yards after treatment

 When to drench

A worm egg count (WEC) is the best practical guide currently available to decide on the need for treatment. Worm egg counts tell you whether worm burdens are likely to be affecting production and will highlight potential worm problems, often before any signs such as scouring, anaemia or obvious weight loss become visible.

Regular worm egg counts, coupled with drench resistance testing allows good planning and effective treatment if needed.

A good professional adviser will assist you in interpreting worm egg counts, deciding when to drench and planning management strategies that reduce drenching and increase sheep productivity.

 Choosing a drench

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 various drench groups 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, such as oral and injectable moxidectin products, closantel products and controlled-release capsules, have persistent efficacy against susceptible target worms.

There can be different delivery methods for worm treatments.

The majority of products are administered as oral drenches but injectable products and controlled-release capsules are other delivery methods used for some products. The withholding period and possibly export slaughter interval of the different products should be considered before using any particular drench.

Drench resistance is a major problem Australia-wide. You cannot assume that all drenches will be effective on your property. A fully effective drench is one that has been shown to be more than 95 percent effective (and preferably should be measured as100 percent effective) in a drench resistance test within the last couple of years. Using a drench that is not effective is usually a waste of time and money and can lead to severe problems with worm control and worsening drench resistance.

However, there are some circumstances where using a drench that is, say, 80% - 90% effective can be useful. You should always seek professional advice before using drenches that are not fully effective.

 Drenching technique

With all treatments there are a few simple tips to help to ensure maximum efficacy:

1. Always read the label on the container of the product to be used.
2. Shake the container to mix the contents thoroughly before use.
3. Ensure that sheep get the correct dose of the product. Weigh a few of the larger animals in the group to be treated and then calculate the dose of the group on the basis of the heaviest weight.
   When using products with a greater risk of toxicity, such as levamisole and naphthalophos on groups of sheep with a wide range in liveweights, divide the animals up into smaller, more uniform groups and treat each with its correct dose to reduce the risk of toxic effects.
4. Double check dose calculations and regularly check drench guns to ensure that you are delivering an accurate dose with a medicine glass or similar device.
5. To administer an oral drench, place the drench gun over the sheep’s tongue rather than in the front of the mouth. This helps to ensure that all of the drench is delivered into the rumen for maximum effect. Injectable products should be administered under the skin (sub-cutaneously) with similar care and technique as that used with vaccinations. Controlled-release capsules should be administered using the applicator designed for the specific product used.

 Holding sheep off feed prior to treatment

Fasting sheep for up to 24 hours before treatment can be used to improve the efficacy of treatments with BZ, ML or closantel products.

Fasting slows the flow of digesta through the gut of the sheep and therefore keeps the drench in the gut for a longer period of time, allowing greater absorption of the active ingredient.

This strategy should not be used when treating with levamisole or naphthalophos as this could increase the risk of toxicity with these products.

Fasting should not be used in heavily pregnant, stressed or poor sheep.

Sheep should have access to water during the fasting period.

 Holding sheep in yards after treatment

Keeping sheep off feed for up to six hours after treatment can assist drench efficacy.

This strategy should not be used on heavily pregnant, stressed or poor sheep, or following treatment with levamisole or naphthalophos as this could increase the risk of toxicity with these products.

Make sure water is available.