How did my horse get worms?
Parasites are an inescapable presence in modern horses. Historically horses free grazed on open pasture, rarely returning to the same location within a year or grazing in close proximity to manure. Today’s horse leads a considerably more confined existence, eating in the same locations and in close proximity to manure. In such settings, the normal symbiotic relationship can spiral into a parasite overload with significant health consequences.
Horses are infected with large or small strongyles when eggs are passed in an infected horse’s manure. Given the proper conditions, these eggs then hatch to larvae and adhere to grass or are shed in water where they are consumed by other horses. The eggs passed in manure do not infect horses; instead they must hatch and mature through three stages before they are ingested to establish an infection.
Animals living in pastures, corrals and fields are more prone to high parasite burdens, as their environment is not as carefully maintained as those who live only in stalls. Performance horses kept in stalls typically see their bedding cleaned daily and replaced regularly. Such maintenance reduces fecal contact and exposure to parasite eggs, minimizing the risk of high parasite burdens. Moreover, stall-bound horses live a comparatively isolated life and are typically only exposed to their own manure — again reducing exposure to parasite eggs shed from other animals. Horses kept primarily in stalls can still exhibit high parasite burdens, but their risk is typically less and effective management is usually much easier.
Pasture kept horses come into contact with manure more regularly, as it is often difficult and costly to pick an entire field on a regular basis. As a solution, many people resort to dragging manure piles across pastures. Manure piles should never be spread across fields, as this essentially distributes parasite eggs over the entire area. Regular manure removal is a healthier option. This will reduce the risk of excessive parasite exposure, but pasture-bound horses typically require more monitoring and care to maintain low parasite levels.
For more on De-Worming, please visit our Health Library Article on our website.