A Longitudinal Observational Study on Lactation-Associated Changes in Procalcitonin, Protein Carbonyl Content, Asymmetric Dimethylarginine, and Symmetric Dimethylarginine in Dairy Cattle.

Procalcitonin (PCT), protein carbonyl content (PCC), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA) have been proposed as promising biomarkers for detecting diseases in cattle. Their concentrations could potentially be influenced by lactation due to oxidative stress commonly observed during this period. This study aimed to evaluate plasma levels of PCT, PCC, ADMA, and SDMA at different stages of lactation in 21 healthy dairy cows: at 15 (T0), 60 (T1), and 150 (T2) days in milk (DIM). Clinically healthy Italian Holstein-Friesian cows were included, selected based on healthy dry periods and weekly veterinary checks during lactation. Blood samples were collected at each time point and biomarkers were measured using validated analytical methods. Data were analyzed using Friedman's test and the value was set at 0.05. Median (IQR) PCT values were 64.29 (40.00-143.23), 75.36 (40.00-161.47), and 77.50 pg/mL (40.00-120.18) at T0, T1, and T2, respectively. PCC medians were 0.17 (0.10-0.27), 0.14 (0.08-0.23), and 0.20 (0.08-0.22) nmol/mL/mg; ADMA values were 0.11 (0.09-0.15), 0.11 (0.09-0.13), and 0.10 µmol/L (0.09-0.14); and SDMA values were 0.11 (0.09-0.14), 0.12 (0.09-0.15), and 0.10 µmol/L (0.09-0.16). No statistically significant differences were observed between time points for any biomarker. These findings suggest that, despite physiological oxidative stress during lactation, these biomarkers remain stable in healthy cows. Therefore, establishing distinct reference ranges based on lactation stage may not be necessary.