title: Effect of dietary ratio of Na:K on feed intake, milk production, and mineral metabolism in mid-lactation dairy cows.
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 3 x 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 33 mEq (Na + K - Cl - S)/100 g of DM. There was a quadratic effect of the ratio of Na:K on DM intake (28.4, 27.5, and 28.3 kg/d for diets A, B, and C, respectively). The ratio of Na:K did not affect milk yield (average 39.2 kg/d), milk composition (average 3.60% fat; 3.01% protein; and 8.62% solids-not-fat), or coccygeal venous plasma concentrations of HCO(3)(-) (average 29.3 mEq/L), Na(+) (average 136.7 mEq/L), K(+) (average 4.53 mEq/L), Cl(-) (average 97.5 mEq/L), Ca (average 10.06 mg/dL), and Mg (average 2.49 mg/dL), and urinary pH (average 8.38) and ratio of Cl(-):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 33 mEq/100 g of DM.
authors.affiliation: Department of Animal and Food Sciences, University of Delaware, Newark 19716, USA.
authors.forename: W
authors.initials: W
authors.lastname: Hu
authors.forename: L
authors.initials: L
authors.lastname: Kung
mesh_terms: D000136:Acid-Base Equilibrium / Q000502:physiology; D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D003612:Dairying; D004032:Diet / Q000662:veterinary*; D004435:Eating / Q000502:physiology*; D004777:Environment; D005260:Female; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D016018:Least-Squares Analysis; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D008903:Minerals / Q000097:blood / Q000378:metabolism* / Q000652:urine; D011188:Potassium / Q000378:metabolism*; D011897:Random Allocation; D012964:Sodium / Q000378:metabolism*; D014556:Urine / Q000737:chemistry
chemical_list: D008903:Minerals; D012964:Sodium; D011188:Potassium