Anthelmintic resistance in sheep nematodes

Many parasitic nematodes of veterinary importance have genetic features that favour development of anthelmintic resistance, this becoming a major worldwide constrain in small ruminant production. The development of anthelmintic resistance poses a large threat to future production and welfare of grazing sheep. Development of variable degrees of resistance among different species of gastrointestinal nematodes has been reported for all the major groups of anthelmintic drugs. Reliable detection of resistance is important, in order to design appropriate strategies for controlling and delaying the development of resistance. Maintaining parasites in refugia and not exposed to anthelmintics, seems to be a key point, because the susceptible genes are preserved. Targeted selective treatments attract the interest of scientists towards this direction. None of the non-chemical methods for parasite control, i.e. nutrition, vaccines, parasite resistant breeds, is sufficiently effective without anthelmintic support and thus do not offer a practical option. However, most of them reduce reliance on the use of chemicals and are environmental friendly. Extensive research is required to manage resistance and field evaluation of any control suggestion. (c) 2008 Elsevier B.V. All rights reserved.