Respiratory disease is the leading health and welfare problem in intensive pig production. Understanding its causes and the role of air quality illuminates systemic welfare failures in commercial pig systems.
Respiratory disease in pigs causes chronic suffering that is partially masked by prey species pain concealment. Pigs with significant lung lesions at slaughter - indicating chronic disease - have experienced ongoing respiratory compromise throughout their growing period. Breathing difficulty, coughing and reduced exercise tolerance are welfare-relevant symptoms that affect quality of life over weeks or months. The high prevalence of respiratory disease in commercial systems reflects air quality and stocking density conditions that are conducive to pathogen spread. Ammonia concentrations that damage pig respiratory epithelia simultaneously damage the respiratory systems of workers in pig buildings - a dual welfare concern rarely discussed in those terms. Reducing respiratory disease through better air quality, lower stocking density and improved biosecurity would simultaneously improve pig welfare and building occupant health.