A key to the identification of arrested gastrointestinal nematode larvae of sheep in Britain

A simple key is presented for the identification of arrested larval nematodes recovered from the gastrointestinal tract of sheep slaughtered in Britain. The parasites included in this key are those species which are most commonly seen to undergo arrested development in sheep. They include Teladorsagia (Ostertagia) spp., Haemonchus contortus, Trichostrongylus axei, intestinal Trichostrongylus spp., Nematodirus battus, Nematodirus filicollis, and Cooperia spp. Easily identifiable morphological features, together with overall dimensions, are used to separate these species.