Interactions of sodium, potassium, and chloride on lactation, acid-base status, and mineral concentrations.

Objectives were to determine responses to graded dietary concentrations of Na, K, and Cl and to cation-anion difference. The design was a partially balanced incomplete block with 48 cows, four 28-d periods, and 15 treatments. Five concentrations each of Na, K, and Cl, ranging from .31 to .85%, .86 to 1.96%, and .32 to 1.15%, respectively, were fed in a TMR based on corn silage. Cation-anion difference (Na+K-Cl) ranged from +12 to +62 meq/100 g of dietary DM. Dry matter intake was affected by interactions between Na and K and between Na and Cl. Yield of 3.5% FCM increased as Na increased (independent of K and Cl concentrations); FCM yield response to dietary K depended on dietary Cl. Milk fat percentage responded quadratically to Na, K, and Cl. Milk fat percentage was maximum at .60% Na, 1.34% K, and .69% Cl. Dry matter intake, BW gain, and blood partial pressure of CO2 responded in a cubic fashion; FCM yield, milk protein percentage, and blood HCO3 concentrations responded quadratically; and blood base excess increased linearly with increasing cation-anion difference. Based on regression models, 3.5% FCM yield and DMI were highest when the cation-anion difference was between +30 and +50. These results indicate that interrelationships among Na, K, and Cl were abundant and were related to blood acid-base status and mineral element concentrations.