Animal health advisors have been urged to assist their customers to conduct a DrenchCheck this summer to determine the efficacy of their proposed sheep drench.
Elanco senior brand manager – sheep Dr Kathryn Humphries says previously published studies have established there is widespread single, double and triple resistance to all older active ingredients, including moxidectin.
“Resistance is recognised as occurring when a drench is unable to reduce the worm burden by more than 95%, with appropriate statistical considerations.
“Despite this, many livestock producers do not know the efficacy of their drench or incorrectly believe it is still fully effective.
“Unfortunately, resistance isn’t ‘black’ or ‘white’.”
“Some drenches might have 90% efficacy; some might have 80% efficacy, and some might have 50%. That means anecdotally, every second customer could be walking out of your store with a drench that’s going to a deliver a sub-optimal outcome.
“The drenches may be ‘working’ to some degree – but any reduction in drench efficacy has a direct impact on the health and productivity of sheep.”
Dr Humphries said it has been long known that even mild or moderate levels of drench resistance can result in a significant economic loss to the producer.
Elanco assisted 70 sheep and wool producers to complete DrenchChecks during 2022, when the producers took the ‘Zolvix Plus Challenge’.
“In 33 of these tests – or almost half, the drench was not fully effective against the worms present in the sheep at the time of testing,” Dr Humphries said.
“Some of the results clearly showed the drench was not working as well as it should.
“In others, it showed the drench didn’t work at all or gave an indication that a specific worm species was highly resistant to that mode of action.
“The advice is simple. If your customer doesn’t know the drench resistance status of the worm population on their property, then they should test.”
Dr Humphries said the 2022 Zolvix Plus Challenge also revealed sub-optimal efficacy in two tests conducted using combination drenches containing the newer active ingredients, monepantel and derquantel.
“No mode of action is immune from resistance, which is why sheep and wool producers should adopt best practice guidelines to protect the efficacy of all available chemistry.”
Dr Humphries said as WormBoss reminds us, “Test and monitor drench efficacy regularly; only use ‘fully effective’ drenches and ideally, combination drenches wherever possible; and only use long-acting products during high worm-risk conditions.”
Elanco is continuing the Zolvix Plus Challenge in 2023.
“We are committed to helping our customers and their advisors to get the best outcome from their investment in animal health products,” Dr Humphries said.
“To participate, encourage your customers to register online at zolvixplusrewards.com.au before their next planned drench.”
A DrenchCheck involves conducting two Worm Egg Count tests to determine the reduction in the worm egg count after drenching.
The first test is conducted before drenching, while the second is conducted 10–14 days after drenching.
The presence of any worm eggs – even very low counts – 14 days after drenching may indicate a problem.
The larval culture results from the second test will indicate which worm species survived treatment and may be resistant to that drench.
A DrenchCheck will provide a “simple, fast and low-cost indication of possible drench resistance”, providing a useful indication of the effectiveness of your existing drench against the worm burden in your sheep at the time of testing.
However, it is a ‘first step’ and does not accurately determine resistance status.
Conducting a full DrenchTest (worm faecal egg count reduction test) every two or three years is regarded as best practice to accurately determine the resistance status and efficacy of each drench class against each worm species.
Dr Humphries said good agricultural practice is essential for optimal worm control and to always read and follow label directions.
