Control of equine nematodes: making the most of faecal egg counts

Helminths are important and highly prevalent pathogens of horses and other Equidae worldwide, particularly nematodes belonging to the cyathostomin group. Helminths have been controlled for over 40 years using broad-spectrum anthelmintics that are often administered in interval treatment programmes, but long-term, frequent use of these drugs has led to the development of drug resistance, particularly in cyathostomins. As helminth infections and worm egg excretion are highly overdispersed among horses within populations, targeted treatment programmes have been promoted to reduce anthelmintic use and, hence, selection pressure for resistance. As part of these programmes, faecal worm egg count (FWEC) analysis is increasingly being used to direct treatment decisions. This article reviews the use of FWECs in equine practice and highlights how FWEC analysis can be optimised to maximise its value in the field.