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

Twelve Ayrshire and eight Friesian cows were randomly assigned to one of fo ur 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-b ase status and feed intake of grass silage based diets during the dry perio d. Four diets provided either 34 g or 74 g total dietary Ca/day, and were e ither 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 wa s formulated using NH4Cl, (NH4)(2)SO4 and MgCl2, as anionic salts. Cows rec eived 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 ca tion-anion balance induced mild metabolic acidosis and increased the abilit y of the cow to maintain blood Ca concentration. However, DCAB should be hi gher since urinary pH decreased markedly (< 6) and so remarkable changes in some blood electrolyte concentrations were noticed.