Short communication: Pro- and antioxidative indicators in serum of dairy cows during late pregnancy and early lactation: Testing the effects of parity, different dietary energy levels, and farm.

Dairy cows face metabolic challenges in the transition from late pregnancy to early lactation. The energy demands for the growing fetus and the onset of milk production are increasing but voluntary feed intake often decreases around parturition and cannot meet these demands. This energy balance, among others, can change the oxidative status. Oxidative stress occurs when antioxidant defense mechanisms are not sufficient to cope with the increasing generation of reactive oxygen species. Our objectives were to investigate (1) the effect of parity on the oxidative status of dairy cows (n = 247) in late pregnancy and early lactation; and (2) the effect of different inclusion rates of concentrate feeding (150 vs. 250 g/kg of energy-corrected milk) during early lactation on 2 farms including 87 cows in total. In addition, we aimed to compare the oxidative status across the 2 farms using equal portions of concentrate feeding. For these purposes, we measured concentrations of the derivatives of reactive oxygen metabolites (dROM) and the ferric reducing ability (FRAP) in serum on d -50, -14, +8, +28, and +100 relative to calving. Furthermore, we calculated the oxidative status index (OSi) as dROM/FRAP × 100. Data were analyzed using a linear mixed model. Cows in the first and second lactations had greater dROM, FRAP, and OSi than cows in their third and greater lactations. Hence, supporting the antioxidative side of the balance might be of particular importance in the first and second lactations. Feeding different amounts of concentrates did not affect dROM, FRAP, or OSi under our experimental conditions, suggesting that the relatively small differences in energy intake were not affecting the oxidative status. Comparing farms, cows from one farm were notable for having greater dROM and lower FRAP, resulting in a greater OSi compared with cows on the other farm. Milk yield showed a time by farm interaction with 7% less milk on d 100 on the farm with the greater OSi. Moreover, cows on that farm had 1.4-fold greater β-hydroxybutyrate concentrations. Our results emphasize the value of assessing oxidative status with regard to both the pro- and antioxidative sides, and support the association between oxidative and metabolic status. Further investigations are needed to determine the applicability of OSi as a prognostic tool during early lactation and to determine which factors have the greatest influence on oxidative status.