Poor air quality in pig housing — characterised by high ammonia, hydrogen sulphide, and particulate levels — causes chronic respiratory disease that is a major welfare concern in intensively managed pig herds.
Indoor air quality represents a pervasive welfare problem in intensive pig housing that is frequently underappreciated because effects are chronic rather than acute. Pigs living in ammonia concentrations of 30-50 ppm — not uncommon in poorly ventilated buildings — experience continuous mild respiratory irritation that impairs mucociliary clearance, reduces immune function, and creates the conditions for pneumonia to establish and spread. The welfare harm accumulates silently over weeks: affected pigs cough more, grow more slowly, and are more susceptible to secondary infections. In extreme cases during slurry agitation — when hydrogen sulphide concentrations can spike to lethal levels — acute mass mortality events have killed hundreds of pigs in minutes. The welfare case for maintaining adequate ventilation is unambiguous, and the economic case is equally strong: reduced feed conversion efficiency and increased disease costs from poor air quality far exceed the investment in proper ventilation design. Monitoring ammonia concentrations with inexpensive sensors provides objective data for management improvement.