Metabolic Profiling of Mammary Vein Blood and Coccygeal-to-Mammary Vein Ratios for Assessing Udder Health in Dairy Cows

Abstract

Inflammation of the mammary gland alters substrate utilization and metabolite trafficking between the systemic circulation and mammary tissue, leading to metabolic adaptations that affect udder function and milk composition. This study investigated mammary metabolic alterations in dairy cows with different udder health statuses by evaluating mammary venous biomarkers (MV), coccygeal-to-mammary vein (CV/MV) concentration ratios, and their associations with milk quality indicators. Sixty Holstein cows were assigned to clinical mastitis, subclinical mastitis, or healthy control groups (n = 20/group). Milk samples were analyzed for somatic cell count (SCC), bacterial load (CFU), and lactose concentration, while blood samples were analyzed for metabolic, enzymatic, and mineral biomarkers, and CV/MV ratios were calculated. Clinical mastitis was associated with reduced MV concentrations of glucose, triglycerides, and calcium and increased concentrations of NEFA, β-hydroxybutyrate, total protein, globulin, urea, bilirubin, and LDH activity. Compared with healthy cows, clinically mastitic cows also showed distinct CV/MV patterns, with ratios > 1 for NEFA, β-hydroxybutyrate, total protein, globulin, AST, urea, and magnesium and <1 for glucose, triglycerides, albumin, ALT, ALP, LDH, and calcium. These shifts in CV/MV ratios demonstrate altered relationships between systemic and mammary venous metabolic profiles across udder health statuses. Principal component analysis clearly separated clinically mastitic cows from healthy animals based on MV biomarkers and CV/MV ratios, whereas subclinical mastitis showed an intermediate metabolic profile. Among the evaluated biomarkers, LDH showed the strongest associations with SCC, CFU, and milk lactose concentration, highlighting its potential as an indicator of intramammary inflammation and tissue injury. The primary novelty of this study is the demonstration that CV/MV ratios provide an additional, potentially useful tool for monitoring mastitis-associated mammary metabolic alterations by capturing changes in the relationship between systemic and mammary venous metabolism. Combining mammary venous metabolic profiling with CV/MV ratios therefore provides complementary information for improved characterization of udder health status in dairy cows.