EFFECTS OF THE ADDITION OF POTASSIUM OR SODIUM, BUT NOT CALCIUM, TO PREPARTUM RATIONS ON MILK FEVER IN DAIRY-COWS

The effects of prepartum dietary concentrations of K, Na, and Ca on th e incidence of periparturient hypocalcemia or milk fever was determine d for older (greater than or equal to 4th lactation) Jersey cows. Cows were fed one of six diets differing in K and Ca contents. In addition , the effect of dietary Na (tested only at the high concentration of d ietary Ca, and low concentration of dietary K) was examined. Treatment s were arranged in an incomplete 2 x 4 factorial design; dietary Ca (0 .5 or 1.5%) and dietary strong cations (1.1, 2.1, and 3.1% or 1.3% Na) were the main effects. Dietary Ca did not significantly affect the in cidence of milk fever or the degree of hypocalcemia experienced by the cows; Milk fever occurred in 2 of 20 cows that were fed the prepartum diet containing 1.1% K and 0.12% Na. Increasing dietary K to 2.1 or 3 .1% increased the incidence of milk fever to 10 of 20 cows and 11 of 2 3 cows, respectively. Increasing dietary Na to 1.3% in the diet contai ning 1.5% Ca induced milk fever in 5 of a cows. Addition of strong cat ions to the prepartum diet increased blood and urine pH and reduced pl asma hydroxyproline concentrations, suggesting that bone resorption of Ca is inhibited in cows fed high K or high Na diets as a result of me tabolic alkalosis. These data demonstrated that dietary Ca concentrati on is not a major risk factor for milk fever and that dietary strong c ations, especially K, induce metabolic alkalosis in the prepartum dair y cow, which reduces the ability of the cow to maintain Ca homeostasis .