Exploring Milk and Blood Biochemical Indicators as Potential Biomarkers of Udder Health in Early Lactation Cows

SCC is a standard indicator of udder inflammation, but it reflects only part of the broader physiological changes occurring in the mammary gland. This study aimed to evaluate associations between SCC, in-line milk traits, and blood biochemical markers in Holstein dairy cows. Based on SCC and California Mastitis Test (CMT) results, 59 cows (20-100 DIM) were divided into three groups: Group 1 (SCC < 200,000 cells/mL; n = 20), Group 2 (SCC 200,000-500,000 cells/mL; n = 19), and Group 3 (SCC > 500,000 cells/mL; n = 20). The Lely Astronaut^® A3 system was used to record milk parameters and behavioral data, while blood samples were collected for biochemical analysis. While there were negative relationships with milk yield (r = -0.266, p < 0.05) and creatinine (r = -0.291, p < 0.05), there was a significant positive correlation between SCC and milk electrical conductivity (EC) (r = 0.330, p < 0.05), gamma-glutamyl transferase (GGT) (r = 0.424, p < 0.001), and lactate dehydrogenase (LDH) (r = 0.285, p < 0.05). Potassium and chloride concentrations varied between groups, indicating slight electrolyte imbalances linked to higher SCC even though they remained within physiological bounds. Receiver operating characteristic (ROC) analysis further showed that milk EC (area under the curve (AUC) = 0.770) and blood potassium (AUC = 0.707) demonstrated the highest diagnostic accuracy for distinguishing healthy and mastitic cows. These results show that integrating SCC data with automated in-line monitoring and blood biochemical profiling can help identify novel complementary indicators for the detection of mastitis in dairy cows and offer a deeper understanding of udder health.