Objectives were to evaluate the effects of feeding diets differing in DCAD (PD = +130 vs. ND = −130 mEq/kg) and source of vitamin D3 prepartum (CH; cholecalciferol vs. CA; calcidiol; both fed at 0.27 mg/kg of diet DM) on Ca status, health, and lactation performance in dairy cows during the transition period. Seventy-nine Holstein cows, 51 parous and 28 nulliparous, at 255 d gestation were blocked by parity, and randomly assigned to 1 of 4 dietary treatments arranged as a 2 × 2 factorial that were fed for the last 21 d prepartum. Dry matter intake (DMI) was measured from 21 d pre- to 42 d in milk (DIM). Prevalence of subclinical hypocalcemia (SCH) was evaluated in the first 3 DIM and defined as blood ionized Ca <1.06 mM. Incidence of diseases was monitored daily for the first 30 DIM. Milk yield and composition were recorded for the first 49 DIM. Data were analyzed using PROC MIXED and PROC GENMOD of SAS. Feeding CA compared with CH increased (P < 0.01) prepartum plasma concentrations of 25OH-D₃ (237.0 vs. 59.5 ± 6.4 ng/mL), 24,25(OH)₂-D₃ (19.2 vs. 1.6 ± 1.0 ng/mL), and 1,25(OH)₂-D₃ (55.3 vs. 48.4 ± 1.7 pg/mL), but decreased that of cholecalciferol (1.7 vs. 15.3 ± 0.5 ng/mL). Feeding ND increased prepartum concentration 1,25(OH)₂D₃ (57.2 vs. 46.9 ± 1.7 pg/mL). The ND diet reduced (P < 0.01) prepartum DMI in multiparous (11.5 vs. 13.7 ± 0.4 kg/d) but not in primiparous cows (11.3 vs. 11.0 ± 0.5 kg/d). Feeding the ND diet reduced (P < 0.05) the prevalence of SCH at 0 and 1 DIM (20.0% and 34.3%) compared with PD (69.3% and 76.5%). Incidence of clinical hypocalcemia (milk fever) was 0% in ND compared with 23.1% in PD cows (P < 0.05). Feeding CA compared with CH reduced (P < 0.05) the incidences of retained placenta (2.5 vs. 30.8%) and metritis (23.1 vs. 46.2%). Cows fed prepartum ND and CA had reduced (P = 0.04) morbidity compared with all other 3 treatments. Cows fed CA produced 3.70 ± 1.2 kg/d more (P < 0.04) 3.5% fat- and energy-corrected milk than those fed CH. The use of prepartum ND in combination with CA improved Ca status, health, and lactation performance in dairy cows.