Small Redworms (Cyathostomins)

These worms are the most common horse parasites.

There are over 50 different species.

Adults living in the large intestine lay eggs that are passed out in the faeces.

The worm eggs hatch and develop through 3 stages. The 3rd stage (L3) is the infective stage. If a grazing horse eats the infective stage the larva will migrate to the intestinal lining where it can remain dormant for long periods of time.

Cyaths in mucosa

Vast numbers of larva can potentially build up in this area. At a later date the larvae will re-activate and erupt out of the gut wall. If large numbers of larvae all do this at the same time it can cause extensive damage to the gut wall. Larvae emerge into the large intestine, develop into adults which lay eggs that are passed out in the droppings thus completing the cycle.