Mastitis remains the most common and economically significant disease in dairy cattle, affecting welfare through pain, fever, and systemic illness. Clinical mastitis causes measurable changes in lying time, feed intake, and social behaviour consistent with acute pain. Prevention science emphasises dry cow therapy optimisation, teat dipping protocols, milking equipment maintenance, and cubicle hygiene. Selective dry cow therapy (SDCT) programmes reduce antibiotic use while maintaining herd health in low-SCC herds. Research demonstrates that cows with subclinical mastitis (SCC >200,000) show reduced milk production and altered behaviour, indicating chronic welfare compromise. Pain management using NSAIDs during clinical episodes is now considered standard of care in many countries.