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Home Drench Resistance Treatment Failure

Treatment Failure

Treatment failure should be distinguished from drench resistance, which is a feature of the worms themselves.

Treatment failure occurs when a drench treatment has failed to control worms due to other factors, such as (click to expand):



  • animals not weighed correctly
  • wide weight range in group
  • applicators not calibrated

Treatment not reaching the worms


  • Drench: e.g. when cattle spit out the drench
  • Pour-On:  not absorbed due to a dirty coat, heavy rain after application, or cattle licking each other

Wrong drench used for the worms

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


  • giving a drench as a pour-on
  • Use of expired products
  • Product not prepared correctly (e.g. a combination/ mixture drench not shaken)

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