Effect of anionic salts in concentrate mixture and calcium intake on some blood and urine minerals, acid-base balance and feed intake of dry pregnant cows on grass silage based feeding

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Twelve Ayrshire and eight Friesian cows were randomly assigned to one of four prepartum diets in a 2 x 2 factorially designed experiment to determine the effect of anionic diet and calcium (Ca) intake on Ca metabolism, acid-base status and feed intake of grass silage based diets during the dry period. Four diets provided either 34 g or 74 g total dietary Ca/day, and were either anionic or cationic. Dietary cation-anion balance (DCAB), calculated as milliequivalents [(Na+ + K+) - (Cl- + S2-)], was -247 mEq/kg dry matter (DM) in the low DCAB group and +34 mEq/kg DM in the high DCAB group. DCAB was formulated using NH4Cl, (NH4)2SO4 and MgCl2 as anionic salts. Cows received grass silage (5.2 kg DM), hay (0.9 kg DM) and concentrate mixture (1.6 kg DM) until calving. Blood and urine samples were collected 4, 3, 2 and 1 week before the expected calving date, at calving, the day after calving and 1 week following calving. The results indicate that the reduction of cation-anion balance induced mild metabolic acidosis and increased the ability of the cow to maintain blood Ca concentration. However, DCAB should be higher since urinary pH decreased markedly (< 6) and so remarkable changes in some blood electrolyte concentrations were noticed.;