Internal parasites cause significant welfare problems in horses, but resistance to anthelmintics is making management increasingly challenging. Evidence-based targeted selective treatment improves welfare while fighting resistance.
Equine parasite management presents a welfare dilemma where undertreatment allows parasite burdens to cause disease and suffering, while overtreatment drives resistance that will eventually undermine all treatment options. The welfare-optimal approach is targeted selective treatment guided by fecal egg counts - treating horses that actually have significant parasite burdens while leaving low-shedders untreated to preserve refugia. This approach requires more diagnostic effort than routine worming but delivers better welfare outcomes through more targeted treatment of horses genuinely at risk, conservation of drug efficacy for future use, and reduction in unnecessary drug administration. Anthelmintic resistance represents a looming welfare crisis that makes evidence-based parasite management urgent.