Lipid status, paraoxonase-1 activity and metabolic parameters in serum of heifers and lactating cows related to oxidative stress.

The objective of this study was to investigate serum lipids, metabolic parameters and activity of the anti-oxidative enzyme paraoxonase-1 (PON1). The study was conducted on non-pregnant heifers with optimal health status and on healthy dairy cows in the period of intensive lactation, assuming that the energy and metabolic demands during lactation reduce anti-oxidative protection. Total cholesterol and HDL-cholesterol concentrations were significantly higher (P<0.05) in lactating cows than in heifers. Bilirubin concentration and γ-glutamyltransferase (GGT) activity were also significantly higher in lactating cows (P<0.05), indicating increased hepatic efforts of cows to meet energy requirements for lactation. Significantly lower PON1 activity and PON1/HDL ratio in lactating cows compared to heifers (P<0.05) showed that metabolic efforts during pregnancy, parturition and lactation influence PON1 activity due to oxidative stress. Concurrent increase in total and HDL-cholesterol during lactation indicated that the HDL particle is a major carrier of cholesterol in cows.