Renal clearance rate, estimated renal reabsorption ratio, and kidney proteome of Holstein dairy cows with divergent milk urea concentrations

Recent mRNA expression studies have proposed various renal proteins to be involved in the excretion of electrolytes, amino acids, and charged compounds to reduce urea, uric acid, and the creatinine clearance rates of dairy cows with high milk urea (HMU) concentrations. Hence, the aim of this study is to analyze the renal clearance of monovalent ions, amino acids and lactate, and the kidney proteome of dairy cows with high and low milk urea concentrations. HMU cows had higher plasma carnosine concentrations but lower renal carnosine clearance and transporter expression. HMU cows possessed increased plasma citrulline but reduced arginase abundance, suggesting downregulated urea detoxification. Pathway analysis revealed proteasomal activation to increase the degradation of proteins which could clog the filter barrier in HMU cows. However, reduced urea, uric acid, and the creatinine clearance rates of HMU cows could not be explained by reduced expression of their transporters but by altered local solute, such as carnosine handling and a lighter relative kidney weight.