In vitro differential neutrophil phagocytosis activity on Staphylococcus aureus when obtained from blood and milk of dairy cows in early lactation period

The ability of bovine blood and milk neutrophils (PMN) to phagocytize fluorescein conjugated Staphylococcus aureus was assessed in 14 clinically healthy dairy cows in early lactation period during 4-6 weeks. Hypotonic erythrocyte lysis (HEL) was used for granulocyte cell isolation from blood and increased leukocyte concentration from milk was induced by intramammary perfusion of Escherichia coli 0:26:B6 lypopolysaccharide B (LPS). A greater in vitro mean phagocytosis index 7.34 ± 1.55 was observed in blood PMN in comparison to milk cells 4.71 ± 1.31 (p < 0.001). PMN phagocytosis ability in blood was 86.5 ± 9.6%, compared to reduced milk cell ability (P < 0.01). The linear relationship between blood and milk cell phagocytosis was y = 0.84 x+ 3.37 (R2 = 0.3783) with association of cell phagocytosis activity (r = 0.615). It is concluded that PMN concentration cells obtained by erythrocyte lysis and LPS udder stimulation are useful for in vitro reproducible phagocytosis assays. These findings are consistent with mammary gland response which induced rapid migration of blood cells. The procedure may facilitate the evaluation of early innate immune response against intramammary bacterial infections in dairy cows.