DIETARY MIXTURES OF SODIUM-BICARBONATE, SODIUM-CHLORIDE, AND POTASSIUM-CHLORIDE - EFFECTS ON LACTATIONAL PERFORMANCE, ACID-BASE STATUS, ANDMINERAL METABOLISM OF HOLSTEIN COWS

The objective of this study was to determine lactational, blood minera l, and blood acid-base responses to dietary mixtures of NaHCO3, NaCl, and KCland dietary cation-anion difference by lactating dairy cows. Th ree 100:0:0 (primary) blends, three 50:50:0 (binary) blends, and one 3 3:33:33 (tertiary) blend of NaHCO3, NaCl, and KCl, respectively, were formulated to replace 1% of the dry matter in a diet based on corn sil age. Seven treatments were defined according to a simplex-centroid mix tures design using a partially balanced incomplete block arrangement. An eighth treatment served as a control and contained 1% SiO2 instead of the mineral blends. Dietary cation-anion difference ranged from +25 to +40 meq of (Na + K - Cl)/100 g of dietary dry matter. Diets were f ed for three consecutive 28-d periods during summer to 36 midlactation cows. Cows that were fed the tertiary mixture had lower milk protein percentage, whole blood bicarbonate, and plasma K than did cows fed th e other blends. With the exception of milk protein percentage. and bod y weight gain, none of the mixtures had a significant impact on lactat ional performance. The lack of differences could have been due to the narrow range in the dietary cation-anion difference studied.