How to drench?
21 May 2015
The three fundamentals of drenching sheep for worm control are:
- Do I need to drench – and if so, when?
- Which drench to use?
- How to drench?
Funded by MLA, WormBoss is in the suite of ParaBoss tools (which include lice and fly management). For successful drenching, WormBoss suggests following these steps where possible:
1. Avoid unnecessary drenching, especially with:
- adult sheep
- during droughts or prolonged dry periods
- immediately before or after moving sheep onto very clean, low worm-risk paddocks (such as ungrazed cereal stubbles or paddocks that have been sheep-free for extended periods)
2. Calibrate drench guns to ensure the correct dose is delivered.
3. Calculate the dose based on the heaviest animals in the mob. Split mobs for drenching if there is a large weight range, so sheep are not under-dosed.
4. Follow the label instructions to ensure correct dose and use of treatments.
5. After sheep have been drenched, graze them initially on paddocks already contaminated with worms likely to be less resistant to drenches (except in the cases of paddocks that are specifically being prepared as low worm-risk). Eggs from surviving drench-resistant worms will be diluted by eggs and larvae already on the paddock and therefore not exposed to the drench (i.e. ‘in refugia’).
If sheep must be drenched onto low worm-risk paddocks, such as lambing, weaning or winter weaner paddocks, do both of the following:
- When the sheep eventually leave these low worm-risk paddocks, treat them with an effective drench that is from a different group to the drench used when the sheep first went onto the paddock. The aim is to remove any drench-resistant worms surviving in the sheep after the first drench.
- Ensure that the next time the paddock is grazed it is with a different mob of sheep. This second mob should have at least a moderate worm burden and their last treatment must be different from the treatment used on the first mob that grazed the low worm-risk paddock. This will dilute drench-resistant worms already on the paddock with more susceptible worms that the second mob is carrying. Note that grazing with cattle will not dilute the proportion of drench-resistant worms, but they will decrease the total number of worm larvae on this paddock.
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