Effects of altering prepartum and postpartum dietary cation-anion difference on calcium concentrations and blood metabolites of Holstein dairy cows.

We determined effects of pre- and postpartum dietary cation-anion difference (DCAD) on urine pH, serum calcium and hormone concentrations, and milk production with 48 multiparous Holstein cows (average body weight = 706 ± 7.3 kg). Treatments were 3 prepartum DCAD concentrations (0, -100, or -180 mEq/kg dry matter [DM]) and 2 postpartum DCAD concentrations (+250 or +350 mEq/kg DM) starting 29 days before parturition through 90 days in milk. Prepartum urine pH was lower (p < 0.05) for -180 than for -100 or 0 DCAD, and postpartum urine pH was higher (p < 0.05) for +350 than for +250 DCAD. Prepartum serum total and ionized calcium and hydroxyproline were greater (p < 0.05) for -180 than for -100 and 0 DCAD, whereas parathyroid hormone was greater (p < 0.05) for 0 than for -100 and -180 DCAD. After calving, negative prepartum DCAD increased (p < 0.05) serum total and ionized calcium, but effects varied by sampling day. Pre- and postpartum DCAD did not affect milk yield or milk fat, but milk protein percent and total solids were increased (p < 0.05) by negative prepartum DCAD. Feeding an acidogenic diet prepartum improved postpartum calcium status without major effects on milk yield and composition.