Air quality in intensive pig buildings directly affects respiratory health and welfare. Ammonia, dust, and pathogens in poorly ventilated barns cause chronic suffering for millions of pigs.
Chronic respiratory disease in indoor pigs represents one of the most pervasive and underacknowledged welfare problems in intensive pig farming. Pigs breathing ammonia-laden air throughout their lives experience continuous irritation of the eyes and respiratory tract, predisposing them to pneumonia and other respiratory conditions. The welfare harm is insidious because it is chronic and cumulative rather than acute and visible. Air quality improvements through lower stocking density, better ventilation design, and bedding provision that reduces ammonia production deliver welfare benefits alongside economic gains from reduced respiratory disease costs. Outdoor and free-range systems with access to fresh air represent the most complete solution but require structural changes to conventional intensive production.