Pinworms are a common topic for questions from our clients. They are not harmful to your horse but their lifecycle can cause significant irritation.
Pinworms, Oxyuris equi, are small roundworms that live in your horses large intestine. The females migrate from here to the anus where they lay their eggs on the skin surrounding it. It is these sticky eggs that irritate your horse and can cause them to rub and itch around the base of their tail and anus. These eggs can hatch and be infective within a few days or drop off and remain dormant for months in the environment.
Unlike many other worms, pinworms cannot be detected using a faecal egg count.
Pinworms are sensitive to the same drugs that you would use in a regular worming program. Ivermectin, moxidectin, fenbendazole and pyrantel are all usually effective. If you are treating for pinworm you should also wash your horses perineal region (anus and area under their tail) regularly to remove any existing eggs.