Paraoxonase 1 in bovine milk and blood as marker of subclinical mastitis caused by Staphylococcus aureus.

The aim of this study was to determine serum lipid values and parameters of oxidative stress in blood and milk of cows with subclinical mastitis (SCM) caused by Staphylococcus aureus and to establish association between these parameters. The study was performed on total of 104 cows assigned into control group of healthy animals (n = 12) and two groups of cows with SCM, either SCM1 group (n = 37) with ˂ 1000 CFU/mL of S. aureus or SCM2 group (n = 55) with ≥1000 CFU/mL of causative agent in milk. Significantly lower serum concentrations of high density lipoprotein-cholesterol (HDLC) in SCM2 group and higher low density lipoprotein-cholesterol (LDL-C) in both SCM groups were recorded. Significantly lower paraoxonase-1 (PON1) activity and higher lipid hydroperoxides (LOOH) concentration in blood and milk were recorded in both groups of SCM cows vs control. In blood serum of cows from SCM2 group significantly higher concentrations of hydrogen peroxide (H2O2) and malondialdehyde (MDA), but significantly lower total antioxidative capacity (TAC) were obtained. In milk serum of SCM cows were detected significantly higher concentrations of H2O2 and MDA, but significantly lower TAC vs control. There was a significant positive correlation between PON1 in serum with HDLC, but negative correlation with LDL-C and LOOH. In milk, PON1 negatively correlated with LOOH and somatic cell counts (SCC). Strong positive correlation was obtained between PON1 in blood and milk. Oxidative stress and inflammatory reaction induced by SCM significantly lowered PON1 activity in blood and milk of affected cows.