Influence of oxidative stress and metabolic adaptation on PON1 activity and MDA level in transition dairy cows.

Serum PON1 is a HDL-associated enzyme that protects lipoproteins, both LDL and HDL, against oxidation and it is considered as an antioxidative/anti-inflammatory component of HDL. Dairy cows are highly susceptible to oxidative stress which commonly occurs in late pregnancy and early lactation. During the transition period, increased production of reactive oxygen species is associated to processes of metabolic adaptation to a low-energy balance. We investigated serum paraoxonase-1 (PON1) activity and malondialdehyde (MDA) concentration to assess the antioxidative/prooxidative status during pregnancy and the postpartum period. In order to evaluate metabolic homeostasis, common metabolic parameters (glucose, triglyceride, total cholesterol, HDL-C and albumin concentrations) were determined as well. A significantly lower PON1 activity was found in late pregnancy and early postpartum (P<0.05) compared to the first and the second trimester of pregnancy and the mid-lactation. MDA level was significantly higher (P<0.05) in the dry period compared to pregnant lactating and postpartum cows. Serum glucose concentration (P<0.001) was lower in the early and late puerperium indicating low-energy balance in the early lactation. Serum triglyceride and albumin concentrations were lower in late puerperium (P<0.001), while total cholesterol and HDL-C were lower during the dry period (P<0.05) as well as in early postpartum (P<0.001). Significant correlations of PON1 activity with glucose (P<0.05), albumin (P<0.05), total cholesterol (P<0.001) and HDL-C (P<0.001) were also found. The observed lower serum PON1 activity and higher MDA level in late pregnancy and early postpartum could indicate a prooxidants/antioxidants imbalance influenced by reproductive stress and metabolic adaptation in the transition period of dairy cows.