The development of a Comprehensive Index (Oxiscore) to assess the Oxidative Status in Periparturient Dairy Cows
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This study introduces an Oxiscore for dairy cows by combining various oxidation and antioxidant markers to measure oxidative stress in clinically healthy periparturient dairy cow. The Oxiscore is defined by subtracting a ‘damage score’ from a ‘protection score’. To obtain the ‘damage score’, levels of determinable reactive oxygen metabolites and thiobarbituric acid reactive substances in plasma are combined. To obtain a ‘protection score’, levels of superoxide dismutase in plasma, selenium-dependent glutathione peroxidase in both plasma and erythrocytes (packed cell volume) and thiol groups in erythrocytes are combined. No dietary antioxidants, like α-tocopherol, or pro-oxidants, like iron, were taken into account. Data from sixteen periparturient dairy cows were used. From these cows, blood samples were taken from the jugular vein at day 30.4 ± 2.0, 24.7 ± 2.4, 17.6 ± 2.2, 10.8 ± 2.2, and 3.9 ± 1.6 antepartum and at 4, 11, 18, 25, and 30 days postpartum. The Oxiscore showed a significant decrease (P = 0.046) only in cows with a mean body condition score above 2.5 between 4 days antepartum and 25 days postpartum. Further, the Oxiscore is significant higher (P = 0.002) in cows with a non esterified fatty acid concentration above 0.4 mmol/L than cows with concentrations below 0.4 mmol/L, but the difference between cows with a β-hydroxybutyrate concentration higher and lower than 0.9 mmol/L was not significant. Regression analysis showed that none of the single markers contributed significantly to the Oxiscore consistently at all sampling days. Due to the small test population and physiological variation of the markers in these healthy subjects the predictive value of their contributions to the Oxiscore requires further study, in which healthy animals that have oxidative stress, healthy animals that do not have oxidative stress and animals that develop disease should be included for validation.Also, reference values of the various biomarkers have to be determined. This would facilitate the determination of the sensitivity of the individual markers and of the Oxiscore in the detection of changes in the oxidative status and thus the value of the Oxiscore in practice.