The common name for ostertagia is brown stomach worm. Ostertagia ostertagi, commonly known as the medium or brown stomach worm, is an important parasitic nematode (round worm) of cattle. O. ostertagi can also be found to a lesser extent in sheep, goats, wild ruminants and horses. The species causes ostertagiosis, which is potentially fatal in cattle.
It is found worldwide and is economically important to cattle industries, particularly those found in temperate climates. O. ostertagi has a direct life cycle, which consists of two stages: the free-living stage on pasture (pre-parasitic) and the parasitic stage in the host (e.g. cattle).
