Acid-base status, renal function, water, and macromineral metabolism of dry cows fed diets differing in cation-anion difference

Abstract Dietary cation-anion difference was defined as the summation of the milli-equivalents of Na and K minus the sum of the milliequivalents of Cl and S per kilogram of DM. Twelve Holstein cows were used in a crossover experiment to compare the effects of changing the cation-anion difference of a diet based on haylage. Two cation-anion differences, 481.8 and 327.2meq/kg, were compared. Increased dietary cation-anion difference had no significant effects on BW or intake and digestibility of DM, ADF, NDF, and N. The diet with a cation-anion difference of 481meq/kg of DM increased apparent absorption of water and urine volume. Fecal excretion of Na and absorption and urinary excretion of S were increased by a cation-anion difference of 327meq/kg of DM. Although blood concentrations were unaffected, lower dietary cation-anion difference reduced concentration of H + and HCO 3 − in urine and total urinary excretion of HCO 3 − . Plasma volume, packed cell volume, glomerular filtration rate, and effective renal plasma flow were unaffected by diet. Small changes in dietary cation-anion differences, even within the positive range, affected acid-base status and water metabolism of dry pregnant cows without affecting renal function or blood volume.