The nutritionaland production costs associated with the development of a competent immune responseagainst nematode parasites is described, based on data from sheep. Anorexiaand changes in metabolism are considered to be driven by the host immune responseitself and the question is raised about the wisdom of seeking to strengthenimmune responses by genetic selection. Several phases of the immune responseare identified with different implications for loss of productivity and opportunityfor moderation of immune responses and production losses by nutrition. Manyanimals are able to manage nematode infections with little loss of productivity.In an era when attempts are being made to reduce anthelmintic use and createrefugia to reduce the rate of development of drench resistance, treatments basedon individual animal performance relative to production targets set by assessmentof the prevailing nutritional environment will become more common. These developments,have already occurred in relation to the haematophagic nematodes, for examplethe "Famacha" technique. Computer-aided weighing and drafting has potentialfor use with the less pathogenic nematodes prevalent in temperate regions thoughwe need to know more about the pathophysiology and nutritional costs of infectionswith Nematodirus spp.
