Relationships between HVT load in feathers and serum antibody titers through a PCA. PCA factorial plot for which three variables used were: HVT load in feathers, anti-NDV Ab titer by HI and Ab titer by ELISA. This plot is highlighting the chicken line groups. All individuals at all weeks, for which the data were completed were plotted. The barycenter of each chicken line group is represented by an enlarged and filled forms: blue dot (Fa), red triangle (He), brown square (Nu), and green cross (pH).