Resistance to worming treatment is an increasing concern amongst horse owners. Resistance occurs because a very small percentage of worms always had a genetic ability to survive chemical treatment; a strategic approach to worming is important to minimise the risk of resistance occurring.

Reasons for resistance:

       Worming too frequently can increase chances of resistance. 

  • Under-dosing or using the incorrect active ingredient can increase chances of resistance 
  • If an infestation of worms is not exposed or affected by treatment, resistance amongst this population can occur slowly over time. 
  • Overgrazing and overstocking of pastures can increase resistance amongst the parasitic populations.