Gastrointestinal parasites cause significant welfare suffering in sheep and the growing resistance to anthelmintics requires strategic management approaches.
Sheep with heavy worm burdens experience anaemia, diarrhoea, weight loss, and bottle jaw (submandibular oedema). Haemonchus-associated anaemia can kill susceptible lambs within days. Parasite-related welfare suffering affects millions of UK sheep annually. The crisis of anthelmintic resistance means that treated animals increasingly fail to be protected, allowing parasites to proliferate and cause welfare harm. Integrated parasite management through strategic treatment, refugia management, and monitoring is both a welfare and sustainability imperative.