Ensuring that the worms in our horse are effectively controlled means that the choice of wormer for your horse is important. Here’s how to resist the resistance!
1. If you’re rotating wormers each grazing season, ensure you change the active ingredient – don’t just switch brand names.
2 Don’t rotate between wormers that belong to the same chemical family. There’s no point rotating between ivermectin and moxidectin-based wormers as both belong to the same chemical family. Worms develop resistence to moxidectin more slowly than ivermectin, so moxidectin-based wormers should be your first choice when choosing a wormer from this family.
3 Check with your vet that there’s no confirmed resistance in your area to the active ingredient you plan to use.
4 Give your horse the correct dose according to his bodyweight. Weight can be assessed by means of a weightape or weighbridge.
5 Reduce usage of wormers by worming less frequently. This can be achieved in two ways: firstly by using wormers with longer dosing intervals; moxidectinbased wormers have a 13 week dosing interval. Secondly, by using faecal worm egg counts and only treating horses when the worm egg count in the horses’ droppings reaches a certain level, normally above 200 eggs per gram.
6 Poo pick. By removing horse droppings from your pasture you’re removing most of the worms that have managed to survive your horses’ worming treatment. These worms are the ones that are – or have the potential to become – resistant to the active ingredient that was used at the time of treatment. By removing these worms, they are unable to reinfect your horse, and so are not able to complete their life cycle, nor produce resistant offspring.