Influence of sodium chloride or potassium chloride on systemic acid-base status, milk yield, and mineral metabolism in lactating dairy cows.
Our objective was to evaluate the response of lactating dairy cows to dietary Na, K, and Cl while holding cation-anion balance constant. Fifteen lactating Holstein cows, blocked according to age and previous milk yield, were assigned randomly to replicated 3 x 3 Latin squares with experimental periods of 3 wk. Diets contained sorghum silage and concentrate in a 40:60 ratio (DM basis) and were formulated to provide +32 meq of [(Na + K) - Cl]/100 g diet DM via one of three variations: 1) basal concentrations of dietary Na, K, and Cl, 2) basal diet with addition of 20 meq of Na and 20 meq of Cl/100 g in the form of 1.17% added NaCl, or 3) basal diet with the addition of 20 meq of K and 20 meq of Cl/100 g in the form of 1.56% added KCl. Free proton concentration in blood was increased by addition of NaCl and KCl; however, this increase did not appear to be physiologically significant, and no other measures of acid-base status were significantly affected. Plasma K was higher and plasma Mg was lower for the diets with supplemental NaCl or KCl than for basal diet. Urine mineral excretion reflected dietary mineral concentration, except Ca and Mg excretion rates were reduced by feeding the KCl diet. Milk yield reflected DM intake, which was lowest with supplemental NaCl. Results of this study indicate that, at a dietary cation-anion balance of +32 meq/100 g of diet DM, the balance of Na and K to Cl in the diet is a more important determinant of dietary impact on systemic acid-base status than actual dietary concentrations of Na, K, and Cl.