Dynamics of metabolic and oxidative stress parameters in dairy heifers during transition period

Dairy cows in early postpartum period experience a rapid increase in milk yield, whereas animal feed consumption ability rises slowly and can not follow increased needs for nutrients (Eicher, 2004). Therefore dairy cows enter a period of negative energy balance (NEB) and metabolic stress. NEB is associated with the change in body condition score (BCS) and the rise of some metabolites such as non-esterified fatty acids (NEFA) and beta- hydroxybutyrate (BHB) (Lassen and Fettman, 2004). Intensified energy metabolism during periparturient period is accompanied by enlarged rates of reactive oxygen species (ROS) production and may results in oxidative stress. Calving causes significant, but temporary, changes in the antioxidant system of cows’ blood (Gaal et al., 2006). Total antioxidant status (TAS) is a single measure that may effectively describe the dynamic equilibrium between pro-oxidants and antioxidant in plasma compartment (Ghiselli et al., 2000). Paroxonase-1 (PON1) is recognized as an important part of the mammalian natural anti-oxidative system (Mackness et al., 1991; Turk et al., 2008).