Abstract # T284

The objective was to evaluate the effects of prepartum preventative Ca strategy, with or without calcidiol, on mineral status and lactation performance. In a randomized controlled trial with a  2 × 2 factorial arrangement, 92 parous cows were assigned at 21 d before expected calving to a negative DCAD diet (-DCAD; -8.2 mEq/100 g of DM) or zeolite A dietary treatment [Z; fed at 2.01% DM, targeting 300 g/d (Nutricow CalBal, Chemlock Nutrition)] with 0 (NoCal) or 3 mg/d of calcidiol (Cal; Nutrivit Puri-D, Chemlock Nutrition). Milk yield was recorded daily and milk composition was analyzed weekly from wk 1 to 4 of lactation. Colostrum was weighed and analyzed for IgG concentration and Brix %. Serum samples collected at -14, -7, -3, 1 to 4, 7, and 14 DIM were analyzed for Ca and P. Cows were retrospectively classified as dyscalcemic if serum Ca was ?2.2 mmol/L at 4 DIM. Data were analyzed using SAS v.9.4 with mixed effects models and repeated-measures analysis, when applicable, and by Fisher’s exact test for dyscalcemia incidence. Calcidiol (2.65 vs. 2.53±0.01 mmol/L; P<0.001) and Z (2.62 vs. 2.56±0.01 mmol/L; P<0.001) fed cows had greater prepartum Ca compared to cows fed NoCal or -DCAD, respectively. Cows fed Z (2.37 vs. 2.19±0.02 mmol/L; P<0.001) and NoCal (2.31 vs. 2.25±0.02 mmol/L; P=0.06) had greater postpartum Ca compared to -DCAD and Cal fed cows, respectively. Cows fed Z-NoCal (1.14±0.06 mmol/L) and Z-Cal (1.26±0.06 mmol/L) did not differ and had the lowest prepartum P concentration and differed from -DCAD-NoCal (1.88±0.06 mmol/L) and -DCAD-Cal (2.39±0.06 mmol/L) fed cows (P<0.001). Postpartum P was lower for Z than -DCAD fed cows (0.93 vs. 1.31±0.04 mmol/L; P<0.001). Zeolite (11.1% vs. 40.9%; P=0.002) and NoCal (11.6 % vs. 39.1%; P=0.004) fed cows had lower dyscalcemia incidence than -DCAD and Cal fed cows, respectively. Milk yield, ECM, 3.5% FCM, and colostrum measures did not differ among treatments. Feeding zeolite A was effective for minimizing dyscalcemia with similar postpartum milk yield as feeding negative DCAD diets whereas calcidiol did not improve production measures.

Keywords: transition cow, calcidiol, zeolite, dyscalcemia