Refugia is the population of worms that is not exposed to wormer treatment so includes the parasites in untreated horses and on the pasture. They pose little threat in small numbers, but serve to dilute the population of treatment-resistant worms. When the treatment-resistant worms breed, they pass on their resistance genes to the next generation. Keeping a population of worms in refugia, however, means that it is not only the resistant worms that breed. In this way the worm population always has a good proportion of treatment-sensitive worms, and worming treatments can continue to be effective now and in the future.
Target worming
One of the best ways to maintain refugia is to use faecal worm egg counts to find out whether your horse requires worming. If you already practice this, you may have noticed that if your horse has a result of less than 200 eggs per gram (epg) you are advised not to worm. This is because a low level of worms is not harmful and actually helps to maintain refugia.
The SMART online planner at www.smartworming.co.uk will help monitor your horses and only treat them if required, thereby helping to preserve the effectiveness of wormers for the future.
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