Effects of altering dietary cation-anion difference on calcium and energy metabolism in peripartum cows

Our objective was to determine the effects of varying dietary cation-anion differences (DCAD: meq[(Na + K) - (Cl + S)l/100 g of dry matter) in prepart um diets on Ca, energy, and endocrine status prepartum and postpartum. Hols tein cows (n = 21) and heifers (n = 34) were fed diets with varying amounts of CaCl2, CaSO4, and MgSO4 to achieve a DCAD of +15 (control), 0, or -15 m eq/100 g of dry matter for the last 24 d before expected calving. Dietary C a concentration was increased (by CaCO3 supplementation) with decreasing DC AD. Plasma ionized Ca concentrations prepartum and at calving in both cows and heifers increased with reduced DCAD in the diet. At calving, plasma ion ized Ca concentration was 3.67, 3.85, and 4.35 for cows and 4.44, 4.57, and 4.62 mg/dl for heifers fed diets containing +15, 0, and -15 DCAD, respecti vely. All heifers had normal concentrations of plasma ionized Ca (>4 mg/dl) at calving. Also at calving, plasma concentrations of parathyroid hormone and calcitriol were less in cows and heifers fed diets containing reduced D CAD, but the plasma concentration of hydroxyproline was not affected by die t. Prepartum dry matter intake, energy balance, and body weight gains were lower and concentration of liver triglyceride was higher for heifers but no t cows fed the -15 DCAD diet. Also, nonesterified fatty acids the last week prepartum were positively correlated with liver triglyceride for heifers b ut not cows. Feeding of anionic salts plus CaCO3 to reduce DCAD to -15 and increase Ca in prepartum diets prevents hypocalcemia at calving in cows, bu t decreases prepartum dry matter intake and increases the concentration of liver triglyceride in heifers. That heifers maintained calcium homeostasis at calving regardless of diet but ate less when fed the -15 DCAD diet sugge sts that they should not be fed anionic salts before calving.