The objective of the present experiment was to evaluate the effect of three different dietary levels of cation-anion balance (DCAB) (+122.1; -8.8; and -110.4 mEq/kg DM) offered for four weeks to groups 1, 2 and 3, respectively, on the plasma levels of ionized calcium (iCa) and total calcium (tCa), the incidence of subclinic hypocalcemia and the urine pH. Twenty-one Holstein cows were assigned to a split plot in time design with seven replications; DCAB was effects in the main plot, and sampling period was effects in the subplot. Plasma samples were collected from the jugular vein at the beginning of treatment and until 12 hours, 1, 2, 3 and 7 days after calf birth (sampling periods 1, 2, 3, 4, 5 and 6, respectively). Urine samples were taken weekly from the beginning of treatment until delivery and were grouped, for the analysis, in three periods. Period 1 is the initiation of the treatment, period 2 extends from 11 to 20 days prepartum, and period 3 extends from 10 days before until the day of delivery. Incidence of subclinic hypocalcemia did not differ between groups. There was no significant effect of treatment or of the interaction between treatment and sampling period on the plasma levels of iCa or tCa, but there was a significant difference on those levels for the sampling period. The lowest levels of both iCa (3.974 mg/dL) and tCa (7.52 mg/dL) were observed at the day of delivery. Urine pH varied significantly among treatments, sampling period and their interaction. Group 3 showed the lowest pH value at sampling period 2 (7.238) compared to period 1 (8.094) and to group 1 (8.045) for the same period. Feeding an anionic diet, by the inclusion of anionic salts to the concentrate feed, had no effect on plasma concentrations of iCa and tCa, reduced urine pH and did not prevent the occurrence of subclinic hypocalcemia.
Key Words: anionic diet, dry cow, milk fever, transition period.
Abstract published in Revista Brasileira de Zootecnia, v.32, n.5, p.1259-1265.