This suggests a longer experimental challenge system which monitors cytokine responses at several time-points may be necessary to establish the relationship between cytokine concentrations and the stage of disease in porcine mycoplasmal pneumonia.Earlier experimental studies in SPF or HDCD pigs have found elevations of these two cytokines in lung lavage fluids at 27 and 32 days (IL-1) or at 14, 21 and 28 days (IL-6)after M. hyopneumoniae infection