Strategies to minimise anthelmintic resistance in large animal practice

AS veterinary surgeons are all too aware, infection with nematodes can cause serious welfare problems in both sheep and cattle, as well as costly production losses. Farmers have become accustomed to being able to control worms with anthelmintics, so the true significance of these parasites may have been largely forgotten. With increased stocking densities and intensive grassland management, nematodes potentially represent a more serious threat than they did before the introduction of broad‐spectrum anthelmintics. It is unlikely that any new anthelmintics will be introduced onto the market in the near future, so loss of efficacy of existing products could pose severe problems for large animal practitioners and their clients. Anthelmintic resistance is already a serious problem in some parts of the world, not just in sheep and goats but also in cattle. A similar situation will develop in the UK unless steps are taken to prevent it. For sheep farmers, it will be, at best, like 'the good old days' when it was unusual to have lowland lambs ready for market before October; at worst, sheep stocking densities will have to be substantially lowered to reduce the risk of animal deaths. This article examines the current extent of the problem of anthelmintic resistance and discusses how it might be avoided.