How Can Drench-Resistant Worms Be Kept Out of Your Property? – Sheep

Keeping drench-resistant worms out of your property is part of sustainable worm control.

Assume that purchased sheep (and those returning from agistment) are carrying worms with some degree of drench resistance to one or more drench groups. See Drench groups and actives.

1. ‘Quarantine’ drench all sheep new to the property.
   • Use a combination of no less than 4 unrelated drench actives with at least one of these being the newest drench actives: monepantel (e.g. Zolvix^®) or derquantel (with abamectin—e.g. Startect^®). This can be done using multi-active (combination) and/or single-active products concurrently—up the race with one product, then up the race again with the next.
   • Do not mix different drenches unless the label states you can or under veterinary advice, as different products may be incompatible.
   • If sheep have come from high rainfall (>600 mm) or irrigation areas in eastern states, consider a liver fluke treatment using triclabendazole.
2. Quarantine the sheep after treatment.
   • Hold the sheep in quarantine in yards (small mobs) or a secure paddock (larger mobs) for 1–3 days (1 day if feed is green high quality, 3 if it is dry low quality) to allow worm eggs present at the time of drenching to pass out of the gut.
   • Provide adequate feed and water.
   • If feasible, keep this paddock free of sheep, goats or alpacas for at least 3 months in summer or 6 months in cooler months.
3. After quarantine, release the sheep onto a paddock that is likely to be contaminated with worm larvae due to grazing by other sheep. This would include most paddocks that have been grazed by home bred sheep for the last 3 months. This will ‘dilute’ (lower the proportion of) resistant worms surviving treatment with worm larvae already on your property.
    
4. WormTest the imported sheep 14 days after drenching for added confidence that treatment was successful.
    
5. Get expert advice on up-to-date recommendations for quarantine treatments (especially if step 3 cannot be achieved). These will evolve as the drench resistance picture changes.