Reducing Resistance to Wormers

Resistance occurs when a selected wormer no longer effectively controls the worm population and it is an increasingly common problem to all wormers.  Once resistance has been established in a worm population, the health, welfare and performance of worm infested horses will be compromised.

Resistance may be increased when too low a dosage of a wormer is used for the weight of the horse, or if the wormer is used too frequently.

To help reduce the incidence of resistance we should:

  • Use faecal worm egg counts to determine whether a wormer is needed. Four faecal worm egg counts are included when you join the Horse Health Programme.
  • Avoid using one particular active ingredient of wormer all the time.
  • Weigh (or weigh tape) our horse/s before dosing and avoid under dosing.
  • Rotate the active ingredient/class of wormer used for each grazing season.
  • Target specific worms with an effective product at the correct time of year.