Managing drench resistance

It is increasing in all drench families (and combinations) and poses a real risk to the viability of livestock farming. The balance of reducing the risk of drench resistance, while still managing worms (internal parasites) so production and animal welfare do not suffer involves compromise.

The risk of drench resistance development can be evaluated and steps taken to minimise it:

• Knowing what drenches are effective on your farm is essential; poor efficacy means lost productivity.
• Continued use of a drench that is losing its efficacy carries a high risk
• The concept of a refugia refers to a worm population not exposed to drenching.
• Well-fed adult stock should not need drenching and can act as a reservoir of non-resistant worms ('Refugia') as well as 'vacuum cleaners' of larvae deposited by young animals.
• Using undrenched animals of the same species to create refugia will ensure there are still non-resistant worms around and this can be a useful tool in delaying resistance.

Drenching should be just one small part of a parasite management plan.