This strategy helps to preserve the effectiveness of your drenches for more years.
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Pastoral: Managing drench resistance
A comprehensive guide to the problem of drench resistance and how it develops; and how you can slow the development.
Testing drench effectiveness with a DrenchTest
How-to guide to check the efficacy of a drench just used.
Checking for drench resistance with a DrenchCheck-Day10
How-to guide to test the efficacy of drenches using a Worm Egg Count Reduction Test (WECRT).
Drench groups and actives
A table listing each of the groups or classes of drench treatments as well as the specific actives in the class, the worms they target and some example products.
Drench mixtures and combinations
An explanation of how mixtures and products differ and why this is important when choosing drenches.
This tool allows you to search for commercial drench products according to various criteria with the results showing a wealth of information including drench resistance notes, withholding periods and dose rates.
For those who prefer a problem based approach to learning, answer the following questions.
Each of the questions below links further down the page to the answers.
You can also click on each question below to go to WormBoss pages with related information.
Each property has its own drench-resistance profile based on its own drenching history and that of properties from which sheep were sourced. The profile of neighbouring properties can be quite different.
The extent of resistance is only known by testing. Obvious worm control failures may only occur when resistance is quite advanced. In this region, a DrenchCheck-Day10 is the preferred method to check individual drenches at any time. DrenchCheck-Day10s should be considered when any drench is given and it is the most practical and cost-effective method of testing drenches in this region.
While a DrenchTest or Worm Egg Count Reduction Test (WECRT) is the most accurate test for drench resistance, this test is rarely feasible in this region as infections are often not high enough and when they are, they may be unexpectedly high and need swift treatment or are in lambs at weaning, which should not be put at risk in aDrenchTest.
The first WormTest within the DrenchCheck-Day10 is done up to 10 days before a mob is drenched with a short-acting drench and the second is done exactly between 10 and 14 days after the mob is drenched (testing earlier or later than 10–14 days can be inaccurate).
3. Name 3 factors associated with choosing and using drenches that can contribute to the development of drench resistance.
*When rotating drenches the current drench would ideally exclude any groups that were used the previous time. However, in practice, ensure the current drench has at least one effective active from a drench group that was not used the previous time.
‘Quarantine’ drench all sheep (including rams) new to the property.
Use a combination of no less than 4 unrelated drench actives with at least one of these being the newest drench actives: monepantel (Zolvix®) or derquantel (with abamectin—Startect®). This can be done using multi-active (combination) and/or single-active products concurrently—up the race with one product, then up the race again with the next.
Do not mix different drenches unless the label states you can, as different products may be incompatible.
A combination contains two or more active ingredients that each target the same worms. The chance of a worm being resistant to all active ingredients in the combination is much lower than for each individual active on its own.
A mixture contains two or more active ingredients, but the actives target different worms. These give the convenience of a single drench when quite different worms are targeted; however, they should be considered 'single-active' against each worm.
Links to the learning topics for Pastoral