How often to de-worm a horse
Traditional de-worming strategies in horses, consisting of rotating the different dewormers at regular intervals, were developed more than 40 years ago and were very effective against Strongylus vulgaris (large strongyle), the most important parasite in horses at the time. However, these traditional programs have led to the development of resistance in other parasite species like small strongyles, which were considered less important at that time but have now become the primary parasite in horses.
Summary
Recommendations
Therefore, recommendations regarding de-worming strategies have changed, and experts now recommend a targeted approach that uses the appropriate de-wormer at the appropriate time, taking into account parasite burdens (fecal egg count) of individual horses.
After determining the fecal egg count, horses are classified as low, moderate, or high shedders (egg releasers), and a decision can be made whether they need to be treated or not.
A certain level of worms can be tolerated without symptoms, and horses should remain healthy if the population of worms is well controlled. Thus, a targeted deworming program aims to reduce pasture contamination by treating moderate and high shedders more often than horses with low contamination potential (low shedders).
Consult your veterinarian about implementing a targeted deworming program at your farm.