INTERACTIONS OF SODIUM, POTASSIUM, AND CHLORIDE ON LACTATION, ACID-BASE STATUS, AND MINERAL CONCENTRATIONS

Objectives were to determine responses to graded dietary concentration s of Na, K, and Cl and to cation-anion difference. The design was a pa rtially balanced incomplete block with 48 cows, four 28-d periods, and 15 treatments. Five concentrations each of Na, K, and Cl, ranging fro m .31 to .85%,.86 to 1.96%, and .32 to 1. 15%, respectively, were fed in a TMR based on com silage. Cation-anion difference (Na + K - Cl) ra nged from +12 to +62 meq/100 g of dietary DM. Dry matter intake was af fected by interactions between Na and K and between Na and Cl. Yield o f 3.5% FCM increased as Na increased (independent of K and Cl concentr ations); FCM yield response to dietary K depended on dietary Cl. Milk fat percentage responded quadratically to Na, K, and Cl. Milk fat perc entage 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 fash ion; FCM yield, milk protein percentage, and blood HCO3 concentrations responded quadratically; and blood base excess increased linearly wit h increasing cation-anion difference. Based on regression models, 3.5% FCM yield and DMI were highest when the cation-anion difference was b etween +30 and +50. These results indicate that interrelationships amo ng Na, K, and Cl were abundant and were related to blood acid-base sta tus and mineral element concentrations.