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These are small (~10mm) reddish brown worms found in the abomasum of ruminants. On a global basis they are the major cause of parasitic gastritis (Ostertagiosis) of ruminants in temperate climates.

The following table lists the three major species.

Nematode Species Host Species Predilection site
Ostertagia ostertagi cattle Abomasum
Ostertagia circumcincta
sheep and goats Abomasum
Ostertagia trifurcata sheep and goats Abomasum

Other, less common species include O. lyrata, and O. kolchida in cattle plus O. leptospicularis found in cattle, sheep and goats.

Ostertagia species are found throughout temperate and subtropical areas of the world.   The cattle species, Ostertagia ostertagi is particularly important in temperate areas wherever cattle are raised.


Adult worms  are  small (approximately 1 cm long) and brownish in color. They are difficult to see at necropsy unless they are present in large numbers (thousands). All parasitic larval stages are found in the gastric glands of the abomasum which must be digested in order to release the larvae for observation with a microscope.

A buccal cavity is present, although tiny, as shown by the linked images from light microscopy and scanning electron microscopy.

The spicules of males are fairly similar in size and shape but are quite distinguishable from spicules of males in other abomasal nematodes (Trichostrongylus axei and Haemonchus).


Parásitos y enfermedades parasitarias de los animales domésticos
Dr. Colin Johnstone (autor principal)
Derechos de copia © Universidad de Pennsylvania