The association of milk cell subsets with management and physiological factors in cows with a natural streptococcal udder infection

Flow cytometry was applied in order to analyse cell content in udder secretions from cows infected by Streptococcus agalactiae (n=10), non-agalactiae streptococci (n=29) and uninfected udder quarters (n=7). Cells were double labelled with anti-CD45 and one of the antibodies specific for granulocytes, CD4, CD8, B lymphocytes or monocytes and analysed by FacsCalibur. The somatic cell count, viability and percentage of labelled granulocytes differed significantly between the infected and uninfected quarters. The association of cell percentages with management and physiological factors were checked using a univariate statistical analysis within each group. Age was associated with viability in the uninfected group, with a percentage of granulocytes in S. agalactiae and the non-agalactiae group. Gravidity was associated with viability in the uninfected group and CD8+ in the non-agalactiae group. Grazing was associated with CD4+ in both the infected groups and with B lymphocytes in the non-agalactiae group. The percentage of CD4+ and CD8+ lymphocytes differed significantly between hand and machine milked animals in the S. agalactiae group. The SCC, the percentage of granulocytes and monocytes varied significantly in regards to breed in the non-agalactiae group.