Whole system approach needed to avoid triple drench resistance | Beef + Lamb New Zealand
Animal Health

Whole system approach needed to avoid triple drench resistance

Triple drench resistance is appearing at an alarming rate particularly in the North Island, but with the correct management, farmers can prevent this occurring.
Wednesday, 11 September 2019

Dannevirke-based vet Simon Marshall, who also the National Spokesman for Wormwise, (New Zealand’s internal parasite management strategy, funded by Beef + Lamb New Zealand) says farmers need to be aware of this emerging issue and while there are plenty of farms where one or more drenches are still effective, farm management strategies need to be implemented to protect long-term drench efficacy.

He defines triple drench resistance as being when a previous susceptible population of parasites can no longer be killed with the same chemical-or in other words, they have developed the ability to withstand that chemical.

Triple combination drenches – which include all three drench families – were released in 2004 and initially proved very effective.

But vets and farmers are now seeing parasites that can withstand all three chemicals and in some cases, this is forcing farmers to completely change their farm systems.

Simon says while using triple-active drenches is a great idea, if the use of these is not coupled with farm management practices that help control internal parasites, then it puts the business at risk of significant productivity and profitability losses.

One of the first steps farmers should take in understanding and managing the internal parasite status on their farm is to establish the efficacy of their drenches with a Faecal Egg Count Reduction Test (FECRT).

Simon recommends doing one of these tests every two to three years in early summer, when most internal parasites are present. If a problem is found, this test may need to be carried out more frequently.

“Some farmers are doing it annually which is a big outlay, but it is recommended otherwise they could be using drenches that are ineffective.”

He admits Faecal Egg Reduction Reduction Tests are a blunt tool, but they show farmers that any changes they have made around their drench use and management have had an effect.  

Faecal Egg Counts can be used strategically to determine worm burdens in individual stock classes such as two-tooths before mating or hoggets over winter.

Even mixed-age ewes can be tested at times of stress such as pre-lamb.

A simple Drench Check – where a FEC is carried out seven to 14 days after drenching – can also give farmers a clue to the efficacy of their drenches. For farmers finishing lambs, doing this test at the start of the season (spring, early summer) will give them an idea of what drench family they should be using that year. 

A larval culture will give farmers an insight into what species of internal parasite they are dealing with on their farm.

“Regular monitoring will help farmers understand the efficacy of their drench programme.”

Simon says all of these tests should be carried out in conjunction with a vet or animal health provider who is able to interrupt the results and advise on any changes in management practices.
Every time farmers use drench, they risk developing resistant worm populations. But taking a whole system approach to the management and control of internal parasites will ideally reduce input costs and allow farmers to use drenches in a more useful and targeted way.

“Taking a whole system approach doesn’t happen overnight and it requires constant monitoring and measuring and potentially making changes along the way.”

In the light of the emergence of triple-drench resistance, Simon recommends all livestock farmers attend a Wormwise workshop or work alongside their vets or animal health professionals to develop a plan to manage internal parasites and retain the efficacy of their drench programme.

Find out more

B+LNZ runs Wormwise workshops. Please contact your local B+LNZ Extension Manager to request a workshop in your area.


Request a copy of the Wormwise handbook, listen to Dave Leathwick’s podcast and keep an eye out for the Internal Parasite management module coming soon on the B+LNZ Knowledge Hub.