Role of sulfur and chloride in the dietary cation-anion balance equation for lactating dairy cattle.
Tucker W.B. | Hogue J.F. | Waterman D.F. | Swenson T.S. | Xin Z. | Hemken R.W. | Jackson J.A. | Adams G.D. | Spicer L.J.
Ten Holstein cows averaging 120 d in lactation were arranged in replicated 5 X 5 Latin squares with 3-wk periods to evaluate the role of sulfur (S) in the dietary cation-anion balance equation. Diets were based on corn silage in Exp. 1 and sorghum silage in Exp. 2. Supplemental S and chloride (Cl) from the double sulfate of potassium and magnesium and CaCl2 were used to manipulate dietary cation-anion balance from 0 to +30 meq when expressed as meq [(Na + K) - (Cl + S)]/100 g diet DM and from +19 to +49 meq when expressed as meq [(Na + K) - Cl]/100 g diet DM. Blood pH was not affected by cation-anion balance, although both S and Cl supplementation tended to lower pH. Blood HCO3(-) and urine pH decreased and plasma calcium (Ca) and urinary Ca excretion increased as anion was added to the diet. Milk fat production tended to be increased by the low S supplementation. Dietary Cl and S had similar effects on acid-base status. Therefore, we suggest that S be included with Cl in the dietary cation-anion balance equation for lactating dairy cows as follows: meq [(Na + K) - (Cl + S)]/100 g diet DM. Although response of acid-base status to S and Cl was similar, as more data comparing the acidogenicity of S vs Cl become available, it may be necessary to include a modifying coefficient for S in the equation to adjust for differences between S and Cl in acid-generating potential. This coefficient may be further dependent on the dietary source of S.
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