Here’s what Horsemen’s Laboratory has found through performing fecal egg counts on horses that are being fed Diatomaceous Earth. In horses that are high shedders, the egg count is often fairly high, 500 strongyle eggs/gm of stool or more. Owners often repeat the test after feeding more Diatomaceous Earth and the results are most often very similar to the first sample. For owners that have a closed herd or only have one horse in a pasture and feeds Diatomaceous Earth we often find egg counts to be very low or negative (no worm eggs found on the counting chamber). These same owners often comment that they clean their horse’s pastures every day or two. Cleaning pastures and removing the eggs before they hatch and become infective larvae has been found to be one of the best practices in the control of worms. Horsemen’s Laboratory has also found that horses that spend most of their time in pastures where the owner cleans on a daily schedule and do not feed Diatomaceous Earth are routinely low shedders to negative and often remain in that category for long periods of time.
Horsemen’s Laboratory does not have hard evidence of the effectiveness of Diatomaceous Earth. It may slow how fast the population of worms multiplies in horses, but it does not appear to completely control worms in horses. That being said, there seems to be many routines and schedules for feeding Diatomaceous Earth and the effectiveness may depend on what routine, schedule and amount that is fed.