Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
2439293 | Journal of Dairy Science | 2009 | 8 Pages |
Abstract
The objective of this study was to determine the effect of altering the dietary ratio of Na:K while keeping the dietary cation-anion difference (DCAD) constant, on dry matter (DM) intake, milk production, and mineral metabolism in lactating dairy cows. Fifteen mid-lactation Holstein cows averaging 160 d in milk were used in a replicated 3Â ÃÂ 3 Latin square design with treatments varying in the molar ratio of Na:K (0.21, 0.53, and 1.06). Diets contained A) 0.25% Na and 2.00% K, B) 0.50% Na and 1.60% K, or C) 0.75% Na and 1.20% K (on a DM basis), and all contained the same DCAD of 33Â mEq (Na + K - Cl - S)/100Â g of DM. There was a quadratic effect of the ratio of Na:K on DM intake (28.4, 27.5, and 28.3Â kg/d for diets A, B, and C, respectively). The ratio of Na:K did not affect milk yield (average 39.2Â kg/d), milk composition (average 3.60% fat; 3.01% protein; and 8.62% solids-not-fat), or coccygeal venous plasma concentrations of HCO3â (average 29.3Â mEq/L), Na+ (average 136.7Â mEq/L), K+ (average 4.53Â mEq/L), Clâ (average 97.5Â mEq/L), Ca (average 10.06Â mg/dL), and Mg (average 2.49Â mg/dL), and urinary pH (average 8.38) and ratio of Clâ:creatinine (average 4.35). The ratios of urinary Na+:creatinine (1.80, 4.21, and 7.42), Ca:creatinine (0.035, 0.041, and 0.064), and Mg:creatinine (0.53, 0.60, and 0.77) increased linearly with increasing ratios of Na:K, whereas the ratio of urinary K+:creatinine decreased linearly as the ratio of Na:K increased (22.4, 15.9, and 10.3). Milk production and composition of mid-lactation cows was similar among dietary ratios of Na:K with the same DCAD of 33Â mEq/100Â g of DM.
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Authors
W. Hu, L. Jr.,