Biomarkers of oxidative stress and liver function in early lactation and their relationship with the reproductive efficiency of multiparous grazing dairy cows in Argentina. A retrospective study.

This study aimed to analyze the possible relationship between days to conception and different oxidative stress (OS) biomarkers and liver functional parameters in multiparous dairy cows. Besides, a fast reliable method for the accurate measurement of malondialdehyde (MDA) by liquid chromatography-tandem mass spectrometry was developed in several matrices. During lactation, the days to conception of 28 cows were determined for a retrospective study. According to this parameter, cows were divided into two groups: high and low days to conception (HDC and LDC, respectively). Blood, urine and liver biopsies were sampled 21 days before the expected calving date, and 7 and 21 days after calving. The method developed for MDA was validated according to international requirements. The lower limit of quantification was 0.25 µmol/L for plasma and urine and 10.00 µmol/L for liver tissue. No differences between groups were observed in the systemic concentration of non-esterified fatty acids, β-hydroxybutyric acid and liver triacylglycerol content (P > 0.05). Cholesterol concentration was higher in the LDC than in the HDC group (P < 0.05). Plasma 3-nitrotyrosine (3-NT) concentration was lower in the LDC than in the HDC group on day 21 post-calving (P < 0.05). Superoxide dismutase activity was higher in the LDC than in the HDC group (P < 0.05). Particularly, in the liver, 3-NT and MDA concentrations were lower in the LDC than in the HDC group (P < 0.05). These results allow inferring that the amelioration of OS biomarkers in plasma and liver could be related to a better reproductive performance of dairy cows.