 The genome size estimate for "O. ostertagi" is ~58 MB, based on "T. circumcincta" ("Ostertagia circumcincta"), whose genome is 58.6 MB and on "H. contortus" at 52 MB, based on flow cytometry.There are 7,006 identified expressed sequenced tags (ESTs), representing 2,564 genes.Clinical ostertagiosis normally occurs in first grazing season calves but can affect mature animals.