Checking for drench resistance with a DrenchCheck
What is a DrenchCheck?
A DrenchCheck provides a simple, fast and low cost indication of possible drench resistance. It is the use of two WormTests—used before and after a drench—to see how the drench reduces the worm egg count.
The first WormTest within the DrenchCheck 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).
Sheep do not need to be yarded for either of the dung sample collections; dung is collected in the paddock as for a WormTest.
If you wish to test mid-length or long-acting drenches, additional follow-up tests should be carried out; seek professional advice on when to do these.
The DrenchCheck is an ideal starting method to check for drench resistance in a single or combination short-acting drench; however it has limitations and a DrenchTest (Worm Egg Count Reduction Test/WECRT) should then be used to correctly determine the presence and extent of drench-resistance in any suspect drenches.
What equipment is required?
- 2 WormTest kits (of the type supplied or recommended by your testing laboratory)
How is a DrenchCheck conducted?
1. Conduct a routine WormTest
- Use the results of a routine WormTest where fresh dung samples were collected in the paddock.
- Ideally, a larval culture should be requested with this WormTest. To avoid an unnecessary larval culture (and cost), you can ask that the culture be done only if the worm egg count is higher than a specified level (i.e. the level at which you would drench).
- If the mob requires drenching, this test will be compared to a WormTest done 10–14 days after drenching.
- This WormTest will be called the ‘WormTest before drenching’.
- If the mob does not require drenching wait until a further WormTest indicates drenching is required.
2. Drench the mob
- Drench the mob within 10 days of receiving results from a WormTest that indicates that drenching is required.
- Any drench (or combination) suitable to treat the worm burden carried may be used.
3. WormTest 10—14 days after drenching
- No sooner than 10 days after the drench and no later than 14 days, conduct another WormTest, collecting fresh samples from the paddock (see ‘Checking sheep for worms with a WormTest’.)
- Request a larval culture regardless of the egg count result.
- Request that the laboratory calculate a DrenchCheck using the results from the ‘WormTest after drenching’ and the ‘WormTest before drenching’ (provide them with the laboratory submission number for the first test).
- Results will be provided as for a WormTest as well as a DrenchCheck result if this has been requested.
- If a mid-length or long-acting drench was used, further WormTests should also be done (ask your testing laboratory for these times).
4. Assess the results of the DrenchCheck
- If the worm egg count results of the WormTest at day 10–14 are not zero or very low, then you should seriously consider more thoroughly investigating the effectiveness of this drench with a DrenchTest (WECRT) or at least continue using the DrenchCheck method if the drench is used again.
- The larval culture results from the WormTest after drenching can also indicate which worm types have lived through the drench and are likely to be drench-resistant.
- If there are worm eggs remaining at the WormTest done 10–14 days after drenching, treatment may be required.
- Seek professional advice to interpret DrenchCheck results and to decide suitable drenches for future use.
* Other WormBoss fact sheets are on the WormBoss web site under ‘Tests &Tools’.