Lipid mobilisation and oxidative stress as metabolic adaptation processes in dairy heifers during transition period.

The objective of this study was to evaluate metabolic disorders and oxidative stress in dairy heifers during the transition period. Possible relationships between lipid mobilisation indicators and oxidative stress markers were investigated as well. Nineteen dairy heifers were included in the study. Blood samples were collected at the time of estrus synchronisation in heifers, at insemination, three weeks after insemination, one week before calving, at calving and 1, 2, 4 and 8 weeks postpartum. Common metabolic parameters, beta-hydroxybutyrate (BHB), free fatty acids (FFA), paraoxonase-1 (PON1) activity and total antioxidative status (TAS) were analysed. Around insemination, no significant difference was observed in the majority of tested parameters (P>0.05). However, the transition period markedly affected the concentration of triglycerides, total cholesterol, HDL-C, BHB, FFA, TAS and PON1activity. Positive correlations between PON1 activity and total cholesterol, HDL-C and triglycerides were noted but inverse correlations with FFA, BHB and bilirubin were found indicating that PON1 activity changed with lipid metabolism and was influenced by negative energy balance. These findings suggest that lipid mobilisation and oxidative stress are part of a complex metabolic adaptation to low energy balance which reaches equilibrium later in advanced lactation.