Novel Active Drench Families and Internal Parasites in Sheep

We have had a very busy drench testing season with some interesting numbers coming out of the properties tested. Efficacy to the three action families varies widely. Those with all three action families still effective are in a strong position for the future. Those with resistance have had to re-think how to manage the production impacts of paratism on the farm. One farmer commented that he could not imagine farming without this information now. It is not all doom and gloom when resistance is detected. It is an opportunity to re-think current practices and apply alternative parasite management strategies.

Novel active drench families- how can we use them in-light of the lessons learnt?

The current role for Zolvix and Startect is as either a quarantine drench to ensure problems are not imported or as an EXIT drench.

Many farmers are now understanding the benefit of giving an EXIT drench in the Autumn to lambs (or ewes that have had single actives in the spring). The concept is that after repeated exposure to a traditional drench type there is the chance that resistant worms may have accumulated in the gut. Cleaning these out (of replacement ewe lambs or winter trade lambs) prior to the winter with a novel active has good logic and will help maintain the effectiveness of the traditional drenches.


This April-May use a novel active drench (Startect or Zolvix) on remaining lambs before the winter.

Dave Robertson BVSc BSc