Local and systemic effects of endotoxin mastitis on the chemiluminescence of milk and blood neutrophils in dairy cows

The local and systemic effects of intramammary lipopolysaccharide (LPS) inj ection on the chemiluminescence (CL) of milk and blood polymorphonuclear le ukocytes (PMN) were investigated in six healthy early lactation cows. Clini cal signs of acute mastitis such as fever, increased heart rate and a decre ased milk production were observed in all cows. Before LPS challenge, the C L activity of milk PMN was significantly lower than that of blood PMN (P < 0.01). A significant negative correlation was found between pre-challenge m ilk and blood PMN CL and, the decreased milk production in unchallenged qua rters. The CL activity of milk PMN from LPS-injected quarters increased fol lowing LPS challenge, whereas it remained unchanged in control quarters. Th e CL activity of blood PMN showed a biphasic increase, with two peaks and a valley below pre-challenge CL activity (P < 0.01). At post-challenge hours (PCH) 6 and 12, the CL activity of milk PMN from LPS-injected quarters exc eeded that of blood PMN (P < 0.05 and P < 0.001, respectively). The decreas ed CL activity of blood PMN and the enhanced CL activity of milk PMN during endotoxin-induced mastitis was reflected by changes in the shape of the CL curve. In blood PMN, a decrease of the second peak of the CL curve suggest s that the myeloperoxidase (MPO)-H2O2 system is impaired during endotoxin-i nduced mastitis. In contrast, the MPO-H2O2 system was enhanced in milk PMN from challenged quarters. The highest duration and intensity of reactive ox ygen intermediate (ROI) production was observed in milk PMN from LPS-inject ed quarters at PCH 12. The increased viability of PMN in LPS-injected quart ers and to a lesser extent in control quarters suggests possible effects of both facilitated diapedesis and inflammatory mediators on milk PMN surviva l. In conclusion, our results suggest that a combination of local and syste mic action of E. coli endotoxin is involved in the priming of milk PMN duri ng mastitis.