ELSEVIER Veterinary Parasitology 72 (1997) 309-326 Immunity development against Ostertagia ostertagi and other gastrointestinal nematodes in cattle J. Vercruysse*, E. Claerebout Faculty of Veterinary Medicine, Laboratoryof Parasitology,Salisburylaan 133, B9820 Merelbeke, Belgium Abstract The immunological response to gastrointestinal nematodes is complex and it will take time and financial support to dissect the different components of protective immunity in ruminants. The present review briefly summarises different aspects and manifestations of protective immunity in cattle against gastrointestinal nematodes, especially Ostertagia os- tertagi, and the factors that may interact with the development of this immunity. © 1997 Elsevier Science B.V. Keywords: Ostertagia ostertagi; Cattle; Nematoda; Immunity I. Introduction The immune response against gastrointestinal (GI) nematodes varies with the worm species, the exposure of the parasite to the host, which is affected by climate, management and control measures, and finally by a variety of host factors which include genetic make-up, age, sex as well as the hormonal and nutritional status. The relative importance of the different GI nematodes differs with host age because of acquired immunity. Normally, a protective host resistance develops against Nematodirus and Cooperia within 1 year. Ostertagia and Trichostrongylus * Corresponding author. 0304-4017/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved Pll S0304-4017(97)00103-9