Oxyuris equi is the scientific name for the pin worm. Adult pinworms, Oxyuris equi, are more common in horses <18 mo old and are found primarily in the terminal portion of the large intestine. The females are 7.5–15 cm long; males are smaller and fewer in number.
The gravid females pass toward the rectum to lay their eggs, “cementing” them to the perineum around the anus. Masses of eggs and cement around the anus appear as a white to yellow, crusty mass. The eggs, which are flattened on one side, become embryonated in a few hours and are infective in 4–5 days.
