Ample phenotypic variation was observed for most traits. The coefficient of variation (CV) was equal to 0.8 on average and ranged from 0.07 to 3.9 (Tables 1 and 2 ). Limited dispersion (CV#0.9) was observed for traits derived from hemograms, cell subsets characterized by fluorescence-activated cell sorting (FACS), phagocytosis capacity and non-specific immunoglobulins. Moderate dispersion (0.9,CV#1.5) was observed for most cytokines produced in vitro except for tumour necrosis factor a (TNFa) and mitogen proliferation-related traits. Finally, the CV for seric C reactive protein (CRP) and haptoglobin (HAPT) levels were close to 1.6 and 2, respectively. The highest CV (3.9) was obtained for the specific IgGs directed against M. hyopneumoniae. These data clearly indicate that the seric inflammatory protein levels and the specific IgGs had the greatest phenotypic variance in our study.