Different responses of oxidative stress index in the plasma of crossbred Holstein cattle during cooling and supplemental recombinant bovine somatotropin

Abstract

The objective of this study was to investigate the effect of supplemental recombinant bovine somatotropin and cooling management on changes in oxidative stress index in the plasma of crossbred Holstein cattle at different stages of lactation. Tenpnmiparous crossbred 87.5% Holstein cattle were randomly divided into 2 groups of five animals each which were housed in Normal Shaded (NS) as non-cooled cows and in shaded with Misters and Fans (MF) as cooled cows. The cows in each group were supplemented of recombinant bovine Somatotropin (rbST) in each stage of lactation with three consecutive subcutaneous injections with 500 mg of rbST in every 14 days. The ambient temperature at 13:00 h in the MF barn was significantly lower while relative humidity was higher than that of the NS barn. Cows under NS barn showed high rectal temperatures and respiration rate as compared with cows under the MF barn. Milk yield significantly increased in both cooled and non-cooled cows treated with rbST in each stage of lactation. The plasma concentrations of Sulfhydryl (SH) residue and Thiobarbituric Acid Reactive Substance (TBARS) did not alter in both groups of cows with or without rbST supplementation but the ascorbic acid concentrations in the plasma and in milk of cows under NS barn were significantly lower than those of cows under MF barn during early and mid lactation. The present study, demonstrates that changes in antioxidant reserve of ascorbic acid in both plasma and milk of dairy cows would be an appropriate and sensitive indicator of oxidative stress in crossbred dairy cows during exposure to high temperatures. © Medwell Journals, 2011.