Zero grazing (fully housed) cattle systems eliminate pasture access year-round, raising fundamental welfare questions about behavioural expression, exercise, and the ability to perform natural behaviours. Research on pasture access demonstrates that dairy cows show strong motivation to access pasture, particularly in spring and autumn, spending 2-4 hours daily grazing when given choice. Outdoor access is associated with lower lameness prevalence, higher activity levels, and improved lying comfort on soft ground. However, well-managed indoor systems with excellent bedding, enrichment, and low stocking density can achieve comparable welfare outcomes on clinical health metrics. The welfare debate centres on whether natural behaviour access is an intrinsic welfare good beyond its instrumental effects. Several countries (Switzerland, Denmark) have introduced mandatory outdoor access requirements. Environmental arguments for indoor systems include precision nutrition, lower greenhouse gas intensity per litre, and land efficiency.