Drench resistance – state of the nation

“Drench resistance a growing problem” – “Triple drench resistance an emerging issue – “Drench resistance a threat”: AgResearch

These are a selection of the headlines you may have seen in rural newspapers in the last 12 months. Certainly, we are fielding plenty of enquiries… “Really?” “Is this for real?” “I hear my neighbour has triple drench resistance” “We don’t have a problem on our place”

One, yes, it is for real, two, sorry but we can’t share your neighbour’s drench test results with you, and unless you have had a recent faecal egg count reduction test, you will not know whether this is problem for your flock or not.


It is real

In the last two years we have diagnosed cases of triple drench resistance in Ostertagia and Trichostrongylus on farms in our practice area. In the main they are well run farms and there is not a bias towards breeding or finishing.

Our colleagues from most parts of the country are reporting similar, with some minor regional variations. It will be interesting as the situation develops to see what might be behind these; there will be both climate and management factors at play.


You won’t know until it’s too late

This autumn there have been cases across the North Island of lamb deaths, with scouring, a week or so after being given a triple combination drench. These have been diagnosed as triple-resistant Trichostrongylus and in each case the farmer had not observed any prior issues with this drench. Some of the cases have been lambs ‘quarantine drenched’ with a triple from a hill country farm, onto a finishing block. There’s a message or two here!

Reductions in lamb liveweight gain generally don’t become noticeable until around 50% of the worms in a population are surviving the drench. If you’re not monitoring this you won’t know and where reduced growth performance is observed it’s normal to look for other causes, if regular drenching is in place. From here it can be a sudden and slippery slope to complete drench failure.


We’re here to help

There are two areas to address in ensuring you have a sustainable worm management plan in place.

Do your Faecal Egg Count Reduction Test (FECRT) – Talk to your vet about getting this sorted. This vital information will tell you where you sit on the drench resistance slope (we have almost no farms where all drenches are fully effective). Armed with this info we can make much better recommendations around product use.

Look at ways in which you can introduce other resistance management strategies

These strategies include:

  • Better feeding and body condition management of adult stock to minimise the need for drench treatment (especially whole flock drenching and especially long acting pre-lamb treatments). Undrenched adult animals can be an important source of non-resistant worms. The farms we work with that have low levels of resistance generally have low or near-zero drench inputs into their MA ewes.
  • Use of the refugia concept – This is deliberately leaving animals within a mob undrenched on each occasion so worms from these ewes or lambs are free to breed without being screened by a drench. There are a number of approaches to implementing refugia and a refugia plan will be quite specific for each farm.
  • ‘Knockout’ drenching – A drench with one of the new actives, administered to lambs that remain on the farm at the end of a summer/autumn drenching programme. This will ‘knock out’ any worms inside the lambs that have been surviving your routine drench. Don’t let them continue to breed.

Farms where ewes are well fed and where the lamb marketing and feed system is complimentary to, and not competing with, the ewe flock, in general can have a much lower annual drench input. Done right, this can greatly minimise the risk of drench resistance, while reducing the impact of worms on production.

To book a faecal egg count reduction test for your flock please give us a call. We are here to provide further information on worm management for your lambs as well as implementing a refugia plan.


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