The effects of changing ration ingredients on acid-base status, renal function, and macromineral metabolism.

Abstract Ten Holstein and 2 Ayrshire cows were used in a switchback design to compare diets based on alfalfa haylage and corn silage. Both diets had a similar cation-anion difference and contained 1% NaHCO 3 . Dietary treatment did not affect DMI, DM digestibility, milk production, or milk composition. Intake, absorption, and urinary excretion of N were significantly increased by the ration based on haylage, but the overall balance remained unaffected. Cows consuming haylage absorbed and excreted significantly more water than did cows consuming corn silage and consequently had significantly larger urine volumes. Blood volume was increased by the ration based on haylage. Intakes of Mg, K, Cl, and S differed between diets, but only K balance was increased by the diet based on haylage. The fractional excretion of K, Cl, and S in urine was increased by the diet based on haylage, demonstrating that the kidneys responded to the increased intakes by diminishing the reabsorption or by increasing the secretion of these minerals. Acid-base parameters for blood, urine, and milk were unaffected by dietary treatment. A diet based on alfalfa haylage, compared with a diet based on corn silage with similar cation-anion difference, resulted in different water and mineral metabolism but did not affect the acid-base status of cows in early lactation.