''Ostertagia spp.'' are small bursate nematodes that parasitse the gastrointestinal tract of mammals and birds. These species are responsible for mortality and morbidity in a number of ruminants especially ''O. ostertagi'' which is widely considered the most important parasite of cattle. | ''Ostertagia spp.'' are small bursate nematodes that parasitse the gastrointestinal tract of mammals and birds. These species are responsible for mortality and morbidity in a number of ruminants especially ''O. ostertagi'' which is widely considered the most important parasite of cattle. |