Effects of Feeding Strategy in Early Lactation on Oxidative Stress of Primiparous Dairy Cows

Oxidative stress (OS) is linked to impaired immune and inflammatory responses leading to metabolic and health problems in the transition dairy cow. The aim of the study was to assess the effect of feeding strategy in early lactation on blood and hepatic tissue OS markers in Holstein cows. Eighteen primiparous cows (528±40 kg BW, 3.2±0.2 BCS, fall calving) were used in a randomized block design with two treatments during the first 65 days postpartum (DPP): (G0) total mixed ration (TMR) ad libitum (17 kgDM/d offered; 70% forage:30% concentrate) or (G1) grazing of alfalfa (Medicago sativa; 6-h am grazing in 3-d strips; pasture allowance=20 kgDM/d) + TMR (70% of ad libitum TMR). Both groups consumed 2.2 kgDM/d of a commercial ration at each milking. Cows were milked twice a day and milk yield was recorded daily. Cow BCS was recorded and blood samples and hepatic biopsies were collected at -7 and +42±3 DPP. Production of reactive oxygen substances (ROS; d-ROMs Test, Diacron, Italy) and antioxidant capacity (SAC; OXY-Adsorbent Test, Diacron) were determined in serum and OS index (OSi) was calculated (ROS/SAC). Expression of 4-hydroxynonenal (4-HNE) modified proteins in liver homogenates was analyzed by Western blotting. Data were analysed as repeated measures with a mixed model including DPP and feeding strategy within DPP as fixed effects and block as random effect. Milk yield was greater (27.5 vs. 25.6 ± 0.60 kg/d; P=0.03) while BCS loss from -7 to +42 DPP was less (-0.50 vs. -0.75 ± 0.03; P=0.04) for G0 than G1 cows. Serum ROS production tended to decreased from -7 to +42 DPP (268.4 vs. 244.6 ± 9.7 CarrU; P=0.058). All cows during the pre and postpartum periods, had SAC values lower than 350 µmol HClO/mL indicating an impairment of serum antioxidant barrier. However, SAC decreased from -7 to +42 DPP only in G1 cows (298.2, 278.8 and 304.4 ± 6.3 µmol HClO/mL for -7 DPP and G0 and G1 at 42 DPP, respectively; P=0.011). Thus, during the postpartum, serum OSi tended to be greater (P=0.09) for G1 than G0 cows (0.92 vs. 0.80 ± 0.05 CarrU/µmol HClO.mL^-1). Presence of 4-HNE in the liver increased from -7 to +42 DPP only in G1 cows (0.73 ± 0.21 and 1.31 vs. 0.81 ± 0.16 for -7 DPP and G0 and G1 at 42 DPP, respectively; P=0.014). Oxidative stress increased during the postpartum in G1 cows associated to a more severe negative energy balance.