Worms in sheep: using drenches

Drench resistance is now a widespread problem throughout Queensland-producers throughout the state have experienced large production losses when their drenches have 'suddenly' let them down during acute infestations that occur from November to March.

Drench resistance can happen after a product has been used often, especially in drier seasons, or when the product has been used inappropriately. It can also happen when drench resistant worms are introduced onto a property. This can be prevented by ensuring that purchased or re-introduced sheep are quarantine drenched.

Using drenches effectively is the key to managing worms and preventing drench resistance. Drenching effectively means:

• not overusing drenches and drenching only when necessary
• selecting the most effective drench for the worm type and your property
• using multi-active drenches and long acting drenches after a period of warm wet conditions
• using single-active drenches in dry seasons and only if necessary 
• using good drenching techniques: follow directions and use the right dose.

When to drench

Use a worm test and take into account weather and paddock conditions when deciding when to drench. The DPI&F WormBuster WormTest report provides advice to help you decide whether drenching is necessary.

Choosing a drench

Cost is no indication of effectiveness. Some 90% of properties in south-east Queensland have shown resistance to the active ingredients in drenches. There is no guarantee that even an expensive 'multi-active' drench will contain a single ingredient that will be effective against the worms on your property.

What works at your neighbour's may not work for you. Each worm population is different, and drench resistance varies from property to property.

There's only one smart way to choose a drench and that's to do what the top producers do: base the decision to drench on the results of a drench resistance test. The test will tell you which active ingredients will work on your property and let you select the most effective and economical drench.

Drench resistance tests should be done once a year, before conditions become favourable for worm infestations usually in about early November but in some years it is often February before worm numbers build up enough to undertake the drench resistance test.

Choosing the wrong drench at a critical time of the year can spell disaster. Producers have lost up to 30% of their stock to acute worm infestations when the drench they used wasn't effective and only produced a slight "knockdown" effect.

More information on the chemical composition of various commercial products is available from 

 Drench List (PDF, 200kB) can be searched on PRODUCT name.

Drenching practices

Good practices will ensure your drenching is effective and economical. You should always:

• Monitor sheep before drenching with a worm egg count.
• Select a highly effective drench based on a drench resistance test.
• Reduce feed before drenching to increase drench effectiveness (BZ and mectin groups only).
• Test the drench gun's accuracy.
• Weigh the sheep so that the dose can be calculated accurately.
• Read the label carefully and follow any precautions or contraindications.
• Use the recommended dose rate and dose to the heaviest sheep in the mob.
• When drenching, place the drench gun over the tongue to increase effectiveness.

More information:

• WormBuster testing service
• Worms in sheep: problem worms
• Worms in sheep: how they spread
• Worms in sheep: quarantine drenching
• Worms in sheep: smart grazing
• Worms in sheep: worm resistant sheep

Who to contact:

• Contact the DPI&F WormBuster Laboratory by phoning the DPI&F Business Information Centre on 13 25 23 between 8 am and 6 pm weekdays or emailing callweb@dpi.qld.gov.au.

Last updated 3 April 2008