Scientific name: Trichostrongylus axei
Common name: Hair Worms

Description: Hairworms develop in the stomach and small intestine. Adult worms are extremely thin and short, measuring only .2 in. (.5 cm) in length. Hair worms attack the tiny, finger-like projections attached to the stomach lining called villi. By damaging the capillaries and lymph vessels within the villi, hair worms decrease the horse’s ability to properly digest food. Severely damaged villi and underlying blood vessels can cause bleeding into the intestines. Bleeding may lead to anemia and poor condition. Foals are especially vulnerable to hair worms and if left untreated, they can cause intestinal bleeding, and the inability to properly digest food.

Life cycle: Horses develop hair worms after eating a food source that has been contaminated with worm eggs. Once ingested, eggs hatch and larvae move to the stomach and small intestine where they mature and lay eggs that pass through manure.

Symptoms: A principal sign of hair worms infestation is dark, fetid diarrhea. Horses with hair worms are usually infected with other parasitic worms and frequently show a lack of appetite and appear run down.

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