Respiratory disease is the leading cause of welfare compromise and economic loss in intensive pig production. Porcine Reproductive and Respiratory Syndrome (PRRS), swine influenza (SIV), Mycoplasma hyopneumoniae, and Actinobacillus pleuropneumoniae (APP) are the primary pathogens. At slaughter, lung lesion scoring reveals prevalence of 30–80% in commercial herds. Welfare impacts include pain, dyspnoea, reduced feed intake, and impaired social behaviour. Prevention relies on vaccination programmes, biosecurity, all-in/all-out production, and air quality management. Ventilation design is critical — inadequate air exchange concentrates pathogens and ammonia. Research demonstrates that pigs in well-ventilated, enriched environments have 40% lower respiratory lesion prevalence. Early detection using cough monitoring systems and biosensor technology is emerging as a welfare improvement tool.