Cyathostomes are a nematode more commonly known as small redworm. They are particularly dangerous to horses and the main cause of clinical disease in equines in the UK.

The adult worm lays eggs in the gut. These eggs are passed in the dung and are visible under a microscope. Faecal egg count analysis is the only definitive method, other than a gut dissection, of detecting an infection.

Small redworm can ‘encyst’ in the gut wall for up to two years. It’s life cycle is suspended, it does not lay eggs and cannot be detected by dung analysis. This is one of the reasons for frequent mis-interpretation of ‘clear’ faecal egg count results.

Many broad spectrum wormers are not effective on the encysted phase. Effective chemicals are moxidectin or a 5 day course of fenbendazole. This is one reason why steps are needed to preserve the effectiveness of moxidectin.