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.