Treatment failure

Drench resistance is a feature of the worms themselves and should be distinguished from ‘treatment failure’, which occurs when a drench treatment has failed to control worms due to factors such as:

  • Under-dosing.
  • Treatment not reaching the worms e.g. when cattle spit out the drench, or a pour-on is not absorbed due to a dirty coat or heavy rain fall after application.
  • The drench used does not target the worm species present e.g. levamisole used to treat inhibited small brown stomach worm (Ostertagia ostertagi).
  • Operator error or mis-application.
  • Use of expired products.