Endogenous Symmetric Dimethylarginine (SDMA) and Asymmetrical Dimethylarginine (ADMA) Levels in Healthy Cows and Cows with Subclinical and Clinical Mastitis—A Comparative Study

Mastitis is one of the most frequent diseases in dairy farms and occurs in both clinical and subclinical forms, resulting in substantial economic losses. Asymmetrical dimethylarginine (ADMA) and symmetrical dimethylarginine (SDMA) are biomarkers that inhibit nitric oxide synthesis. Elevated ADMA levels are associated with an increased risk of mortality both in human medicine and in dogs and a potential need for intensive care, while SDMA correlates with poor prognoses in humans and the progression of renal disease in horses, though its impact varies depending on renal function. This study examines the plasma levels of ADMA and SDMA in healthy cows (H) and cows with subclinical mastitis (SCM) and clinical mastitis (CM). Cows were classified as having mastitis when CMT > 1 and SCC ≥ 250,000 cells/mL. The SCM group showed no clinical signs or milk alterations, whereas the CM group exhibited udder and/or milk changes. The study included 196 blood samples to determine ADMA and SDMA concentrations, with 96 from healthy cows and 100 from pathological cows (58 SCM and 42 CM). The descriptive statistics were reported as the median because the data were not normally distributed (Shapiro–Wilk test). Data were analyzed using the Kruskal–Wallis test with Bonferroni post hoc correction, and the cut-off and accuracy index were calculated using the gold-standard measurement, the SCC. Statistically significant differences in ADMA levels were observed between healthy cows (0.11 µmol/L) and cows with mastitis (SCM 0.26 µmol/L; CM 0.26 µmol/L), but no differences were found in their SDMA levels. The cut-off for ADMA was >0.164 µmol/L, with a sensitivity of 80.41% and specificity of 77.78%. This study suggests that the blood concentration of ADMA is statistically higher in cows with subclinical and clinical mastitis and could be further explored as a potential biomarker for diagnosing these diseases.