Abstract
BACKGROUND: Elevated BHB levels are hypothesized to influence hepatic antioxidant enzyme expression and activity, contributing to oxidative response. However, the impact of BHB between 0.8 and 1.2 mmol/L on these mechanisms remains unclear. We hypothesized that elevated serum BHB levels would influence the hepatic expression of antioxidant genes (SOD1, SOD2, SOD3, and GPX3) and blood antioxidant enzyme activity, contributing to oxidative response. The primary objective was to evaluate the correlation between serum BHB levels, hepatic antioxidant gene expression, and blood antioxidant enzyme activity in high-yielding dairy cows during the postpartum period. The study involved 23 healthy high-yielding Holstein-Friesian dairy cows, divided into experimental (EXP, n = 12) and control (CONT, n = 11) groups based on serum BHB levels during the first three weeks postpartum. The EXP group maintained BHB levels between 0.8 and 1.2 mmol/L, while the CONT group remained below 0.8 mmol/L. All animals were monitored up to 9 weeks postpartum. This cohort study utilized weekly blood samples from 7 days prepartum to 9 weeks postpartum and liver biopsy samples from 4 to 7 weeks postpartum. Serum BHB concentrations, blood SOD and GSH-Px activities, and hepatic expression of SOD1, SOD2, SOD3, and GPX3 genes were analyzed. RESULTS: The EXP group exhibited a significant increase in hepatic SOD2 expression at 4 weeks postpartum (p < 0.05) and higher blood SOD activity at 6 and 7 weeks postpartum compared to controls. This suggests an oxidative activity response to elevated BHB levels. By week 7, hepatic SOD2 expression began to normalize, indicating a transient response or adaptation. No significant changes were observed in hepatic SOD1, SOD3, or GPX3 expression between groups. CONCLUSION: Persistently high serum BHB levels in postparturient dairy cows significantly impact hepatic SOD2 expression and blood SOD activity. The specificity of this response, primarily involving SOD2, highlights the complex interplay between metabolic changes and oxidative mechanisms during the transition period. These findings underline the importance of BHB concentration monitoring and suggest potential reevaluation of current BHB thresholds for identifying at-risk cows. Furthermore, SOD2 could potentially serve as an early biomarker.