Current and future prospects for control of ostertagiasis in northern Europe--examples from Denmark.

This review primarily discusses the status and prospects for control of bovine ostertagiasis in northern Europe, with examples from Denmark. There are different ongoing developments in agricultural systems and practices, and methods and possibilities for practical control depend on the intensity and specialisation of these; the modern dairy farm remains at highest risk of parasitism, owing to increasing stocking densities and limited natural control elements at hand. Epidemiology and course of infections are significantly influenced by the gradual build-up of acquired immunity, which usually contributes to prevent loss-producing effects in second season and older animals. It may be of doubtful value to exaggerate worm control in first season animals, because this may reduce development of immunity with the risk of translocating parasite problems from the young to the older, economically more important age categories of animals. A number of reasons for adopting an overall consideration on worm control and performance throughout adolescence is emphasised. Control by management relies on a fairly detailed insight into local transmission factors of Ostertagia ostertagi and related trichostrongyles. No doubt future investigations will provide important additional knowledge in this area. Anthelmintics will continue to constitute a major control measure, but it is unlikely that there will be any acceleration in the rate of commercial release of new compounds. However, ongoing modifications and new formulations of existing anthelmintics will continue to be produced, and implementation at the farm level of the proper use of anthelmintics and other control measures will be one of the important tasks of the coming century. Until now, the development of anthelmintic resistance in cattle has been negligible, but it may possibly pose a potential risk over the coming decades. With regard to some new anthelmintics that have environmental concerns related to their faecal excretion, this should be carefully examined in the future. Control in the form of vaccination or biological control by microfungi or others would be attractive alternatives that should be given a high research priority. Yet, at present it is not easy to predict which of these may lead to feasible, practical control.