This strategy describes when to use strategic drenches and how to decide when tactical/therapeutic drenches are needed.
For those who like to see all the information and simply read through it in order. Each heading is a link to a page of information—the dot point provides a summary of the page.
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Western Australian winter rainfall: When to test and when to drench
The times for routine worm testing and drenching in this region. Not all testing or drenching is routine; other times to do these are recommended by the Drench Decision Guide, according to details you provide about your mob of sheep.
Western Australian winter rainfall: Drench Decision Guide
This tool recommends whether a mob should be drenched, the length of protection warranted and when to worm test again. It is your day-to-day tool on drenching decisions that should be used in conjunction with the annual program of routine testing and drenching times.
The DDG tool steers you through a series of questions about your sheep; choose the answer that applies to your mob (or make up your own scenario).
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.
1. What is the purpose of a strategic drench?
Strategic drench: a drench given at a critical time to sheep that are susceptible to worm infection (e.g. weaners and pre-lambing ewes) and also given at times to reduce worm larval contamination of a pasture grazed by the drenched sheep over the following weeks or months. The sheep themselves may have had a low worm egg count at the time of this pre-emptive treatment.
In WA, the routine ‘Summer-autumn drench’ program is recommended for the main sheep areas (the South-West Medium to High Rainfall Zone). In the Low Rainfall Cereal Zone, routine treatment is needed only for younger age classes. It is critical that all drenches given in summer and autumn are given with a fully-effective drench, as otherwise drench resistance is likely to increase more rapidly.
The strongly seasonal nature of Mediterranean environments lends itself to a routine drenching program, as dry summer and autumn pastures are unfavourable for worms, and sheep drenched then do not pick up new worm burdens. This is the basis of the highly efficient ‘summer drenching’ program. However, summer drenching has been confirmed as the main factor causing the high levels of drench resistance in WA, as any worms surviving these drenches (i.e. resistant worms) are the source of future worm populations.
To reduce the risk of drench-resistance without affecting the effectiveness of worm control, ‘summer drenching’ should be replaced by ‘Summer-autumn drenching’. (See DAFWA FarmNote No. 348: ‘Sheep worms — a change to summer autumn worm control’ by clicking here, then Animal Health, then Parasites.)
Under this program, drenches for adult sheep are delayed until autumn, and only weaner and hogget-age sheep are drenched in summer. Most adult sheep have low worm egg counts in early summer and a drench at that time is not warranted; delaying a drench until late March or April allows some less-resistant worms to survive. Provided that the worm population on the property includes sufficient less-resistant worms to dilute resistant worms, the overall resistance level on the property will be reduced.
4. The online Drench Decision Guide (DDG) for Western Australia assists you to decide whether a mob of sheep should be drenched now and when to test again. Open the DDG and answer the questions it offers based on the scenario (from below) that you are using. Try at least three of the following scenarios.
Links to the learning topics for Western Australia