SMALL redworms (cyathostomins) are extremely common equine parasites and are increasingly resistant to all available worming medications, particularly fenbendazole and pyrantel, with emerging resistance to macrocyclic lactone wormers. Small redworm larvae can encyst in the gut wall for months, with high burdens leading to larval cyathostominosis, a serious, and sometimes fatal, condition.

To prevent clinical disease in horses that have received ineffective treatments, it is essential to maintain the effectiveness of the existing wormers. This involves applying evidence-based strategies that include assessment of infection risk, paddock hygiene, treating only high-risk horses and using tests to inform treatment decisions.