Pinworms (Oxyuris equi)

Lifecycle: Pinworm larvae mature in the large intestine, feeding off the intestinal lining. Adult females move to the anal area where they lay eggs covered with a sticky fluid that causes severe itching.

How It Gets Into Your Horse: Horses become infected with pinworms when they ingest eggs that have dropped into feed or water.

Dangers If Left Untreated: Heavily infected horses may be nervous and stop eating. The severe itching makes the horse rub its tail and rump so much the tail hairs break off. Rubbing, biting and scratching can open up the skin to infections.