These are generally only a problem in foals as horses develop a natural immunity at around 6 months of age. Larvae are passed to the foal through the mare’s milk, and minimizing infection can be achieved by treating the mare for this parasite, particularly before foaling. However, foals can also pick the larvae up from the pasture themselves. The life cycle is only a few weeks long meaning a heavy worm burden can be acquired very quickly.

Size/Appearance: The intestinal threadworm
is slender and hair-like and up to 1cm long.

Location in Horse: The larvae migrate to the lungs, are swallowed and develop into adults in the small intestine.

Symptoms: Symptoms include diarrhoea, anorexia and dullness as well as a reduced growth rate and loss of weight, which in foals
can result in potential complications in later life.

.