Pinworm Infection

Intestinal parasites are an important cause of death in horses of all types. The prevalence of many intestinal helminths is high and, within any population of horses, certain individuals can harbor large numbers of parasites, which may lead to disease.

Pinworms (Oxyuris Equi)are nematodes that occur in the large intestine of horse throughout the world. The males are small, but the females may reach 4 inches long and are white-gray in color, with a long tail tapering to a point, hence the name pinworm.

Friesian horse

Signs of Pinworm Infestation

The presence of the female worms laying their eggs and particularly the presence of the eggs themselves stuck in a gelatinous mass around the anus are irritating, so affected horses will rub their tails. There are several types of deworming compounds: Ivermectin, Moxidectin, Fenbendazole, Pyrantels (Pyrantel Pamoate), and Quasiquantels. Each compound works differently in the horse to destroy internal parasites. Ivermectin paste administered to horses orally continues to be highly effective for treatment and control of a broad range of small and large strongyle species as well as other species of gastrointestinal parasites.

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Measures are not usually applied specifically for the control of pinworms. Any program of treatment to control the strongyles will control the infection with pinworms. In fact, the presence of pinworms may suggest that the srongyle control program is not being applied properly and the complete worming program should be reviewed. All incoming or returning horses should be quarantine drenched with an effective product. This product should also be able to remove inhibited (and potentially resistant) larvae. Moxidectin appears to have an advantage here. Don't breed from wormy horses. In time this should lead to reduced pasture pollution. Use pasture management. Pick up feces.


  1. Re-evaluation of ivermectin efficacy against equine gastrointestinal parasites.Klei TR, Rehbein S, Visser M, Langholff WK, Chapman MR, French DD, Hanson P.>
  2. Veterinary Notes for Horse Owners. Captain M. Horace Hayes

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