1534 Effects of prepartum dietary cation–anion difference and source of vitamin D on dairy cows: Vitamin D, mineral, and bone metabolism

This 2 × 2 factorial study evaluated the effects of feeding dairy cows diets containing either calcidiol or cholecalciferol (3 mg/11 kg of diet DM) and positive (+130 mEq/kg) or negative (−130 mEq/kg) dietary cation–anion difference (DCAD) on vitamin D, mineral, and bone homeostasis during transition. Pregnant Holstein cows (n = 79) were blocked by parity and milk yield and randomly allocated to treatments from 255 d of gestation until calving. All groups of cows were then fed on identical lactating cow diets until 49 d after calving. Blood samples were taken thrice weekly prepartum and after calving until d 30 of lactation, with additional samples taken at 0, 1, and 2 d postpartum, for analysis. Milk yield and composition were recorded for the first 49 DIM. Feeding calcidiol increased concentrations of calcidiol pre- (235.1 ± 6.18 vs. 60.3 ± 6.25 ng/mL) and postpartum (214.8 ± 4.85 vs. 59.13 ± 4.90 ng/mL) and calcitriol prepartum (55.66 ± 1.62 vs. 51.05 ± 1.64 ng/mL) when compared with feeding cholecalciferol. Feeding negative vs. positive DCAD increased prepartum concentrations of calcitriol (58.0 ± 1.61 vs. 48.3 ± 1.65 pg/mL) but decreased calcidiol (136.0 ± 6.17 vs. 160.4 ± 6.26 ng/mL) and cholecalciferol (6.8 ± 0.41 vs. 9.7 ± 0.42 ng/mL) prepartum and calcidiol, cholecalciferol and calcitriol postpartum (131.3 ± 4.84 vs. 144.4 ± 4.91 ng/mL, 3.7 ± 0.28 vs. 4.9 ± 0.28 ng/mL, and 98.0 ± 4.29 vs. 117.5 ± 4.34 pg/mL, respectively). After calving, calcitriol was higher in parous than nulliparous cows. Blood calcium increased in cows fed calcidiol (2.45 ± 0.02 vs. 2.34 ± 0.02 and 2.27 ± 0.01 vs. 2.25 ± 0.01 mM for pre- and postpartum, respectively). Calcium concentrations in the negative DCAD group were lower before calving, compared with the positive DCAD group (2.36 ± 0.2 vs. 2.43 ± 0.2 mM), but higher postpartum (2.29 ± 0.01 vs. 2.23 ± 0.01 mM). Feeding negative DCAD lowered blood pH (7.44 ± 0.01 vs. 7.49 ± 0.01) compared with positive DCAD prepartum but not postpartum. There was no effect of vitamin D or DCAD on blood osteocalcin, PTH, adiponectin, leptin, or serotonin concentrations. Nulliparous cows had higher blood concentrations of osteocalcin and crosslaps than parous cows. Cows fed calcidiol produced 3.70 ± 1.2 kg/d more 3.5% fat- and energy-corrected milk than those receiving cholecalciferol.