Mycoplasma hyopneumoniae, the cause of enzootic pneumonia, is the most economically important pig respiratory pathogen and a major cause of chronic welfare harm in finishing pigs.
Pigs with enzootic pneumonia experience chronic respiratory discomfort, reduced activity and poor feed conversion. Lung lesion scores at slaughter reveal the historical burden: in conventional systems, mean lung lesion scores indicate widespread subclinical infection. Co-infection with PRRS creates severe acute respiratory disease causing distress, fever and high mortality. Vaccination, biosecurity, all-in all-out housing and positive pressure ventilation are the most welfare-effective interventions available.