Digital dermatitis (DD, Mortellaro disease) is the most common infectious cause of lameness in dairy cattle, affecting 20-60% of cows in endemic herds and causing significant pain and welfare compromise. The condition involves treponema bacteria infecting the skin above the heel, causing painful proliferative lesions graded M0-M4. Lame cows show reduced feeding time, altered lying time, and social withdrawal consistent with chronic pain. Early lesions (M1) respond well to topical treatment (oxytetracycline spray); advanced lesions require bandaging and prolonged management. Collective footbath treatment using copper sulphate or formalin reduces herd prevalence. Biosecurity - preventing introduction through purchased cattle - is critical as DD is highly contagious. Research identifies high stocking density, slurry accumulation, and inadequate cubicle maintenance as primary risk factors. Welfare monitoring programmes use DD lesion prevalence as a key herd welfare indicator.