Dose dependent changes in inflammatory parameters in the milk of dairy cows after intramammary infusion of lipopolysaccharide

The goal of this study was to evaluate the dose dependent changes in common milk and blood parameters for udder health after an intramammary (IM) infusion of five different doses of lipopolysaccharide (LPS, 100, 50, 25, 12.5 and 6.25 μg, respectively). Ten Holstein Friesian cows randomly divided into five groups of 2 cows each were IM infused into one quarter with one LPS dose dissolved in 10 ml of saline. The contralateral quarter was infused with 10 ml saline (9 g/l). Milk samples were taken immediately before and 12, 24, 36, 48 and 60 hours after the treatment. All milk samples were analysed for somatic cell counts (SCC), lactose, sodium (Na), chloride (Cl) and electrical conductivity (EC). Two blood samples were taken immediately after milking for analysing leukocytes (WBC), polymorphonuclear neutrophils (PMN), Na and Cl. The SCC increased maximal at 12 hours after the LPS challenge and differed among LPS doses, as well as the area under curve from 0 to 36 hours (AUC 0-36 h). There were no significant differences among LPS doses in lactose levels for the regression at 12 hours and AUC 0-36 h. Lactose levels in milk from quarters receiving the lowest dose of LPS were lowest after 24 hours, whereas in all other groups lactose levels decreased maximal within the first 12 hours. The regression at 12 hours as well as the AUC 0-36 h showed significant changes for Cl levels but not for Na and EC, respectively. Amongst all groups EC increased maximal within 12 hours and peak EC showed dose dependent differences with highest values at the highest LPS dose. There were no dose differences in WBC. Blood electrolytes showed only tendentially dose dependent differences for blood Na in AUC 0-36 h. The results were possibly due to a great individual variance amongst all cows. In conclusion there are dose dependent differences in the response to LPS especially in milk parameters, which are likely caused by a greater tight junction damage by higher LPS doses. 100 μg LPS seems to be a threshold between low and high doses of LPS. All doses used in this study induced signs of mastitis but there might be a low dose of LPS with only an enhancing effect on mammary gland immune status without inducing mastitis symptoms. This needs to be investigated for developing new ways of mastitis prophylaxis.