Relative acidifying activity of anionic salts commonly used to prevent milk fever

Abstract

High cation diets can cause milk fever in dairy cows as they induce a metabolic alkalosis reducing the ability of the cow to maintain calcium homeostasis at the onset of lactation. Adding anions to the diet can offset the effect of the high cation forages by inducing a mild metabolic acidosis, restoring the ability to maintain calcium homeostasis. The difference in mEq of dietary cations and anions (DCAD) is most often expressed as (Na+ + K+) - (Cl- + S--). This equation implies that a mEq of chloride and a mEq of sulfate are equipotent in their ability to alter acid-base balance of the cow. Using blood and urine pH to monitor effects on acid-base balance, experiments were conducted to test the relative acidifying activity of various sulfate and chloride anion sources in nonpregnant, nonlactating Jersey cows. Across all experiments, chloride proved to have about 1.6 times the acidifying activity of sulfate. Calcium and magnesium, ignored by the common DCAD equation, had a small but significant alkalinizing effect when accompanying chloride or sulfate. The ranking of the anion sources tested at a dose of 2 Eq/ d, from most to least potent urine acidifier, was hydrochloric acid, ammonium chloride, calcium chloride, calcium sulfate, magnesium sulfate, and sulfur. These data should allow more accurate prediction of the response of late gestation cows to dietary cation-anion manipulation.