442 Effects of added 25(OH)D3 with varying standardized total tract digestible phosphorus levels on nursery pig performance, bone and urine characteristics, and serum vitamin D
Authors: Becker Larissa L , Gebhardt Jordan T , Tokach Mike D , Goodband Robert D , DeRouchey Joel M , Woodworth Jason C , Bergstrom Jon R 
Published: September 2024

Abstract
Pigs [n = 360; DNA 600×241; initial body weight (BW) = 5.8 ± 0.54 kg] were used in a 45-d study to evaluate effects of added 25(OH)D3 with three levels of standardized total tract digestible (STTD) P on nursery pig growth performance, bone and urine characteristics, and serum vitamin D status. Pigs were weaned at approximately 19 d of age and randomly allotted to 6 treatments with 5 pigs/pen and 12 replications/treatment. Dietary treatments were arranged in a 2 × 3 factorial with main effects of 25(OH)D3 (0 or 50 µg/kg equivalent to 2,000 IU/kg of vitamin D3; Hy-D, dsm-firmenich, Plainsboro, NJ) and STTD P (70, 100, or 130% of the NRC (2012) requirement on a dietary percentage basis). Diets were corn-soybean meal-based and fed in 3 phases. On d 45, 1 pig/pen was euthanized to collect right fibula, metacarpal, and 2nd and 10th ribs. Overall, increasing STTD P increased (quadratic, P &lt; 0.003) BW, ADG, ADFI, and G/F with minimal improvement above 100% of NRC STTD P requirement. Added 25(OH)D3 had no effect on growth performance (P &gt; 0.10). Pigs fed increasing STTD P had decreased urinary Ca concentration (linear, P &lt; 0.001 and quadratic, P = 0.078) and increased urinary P concentration (quadratic, P &lt; 0.001), with all pigs fed 70% of NRC STTD P requirement having non-detectable levels of urinary P. Added 25(OH)D3 had no effect on urinary Ca and P concentration (P &gt; 0.10). A quadratic 25(OH)D3×STTD P interaction (P = 0.032) was observed for serum 25(OH)D3. When pigs were fed 25(OH)D3, serum 25(OH)D3 increased as STTD P increased (quadratic, P = 0.005) but no differences were observed when no 25(OH)D3 was added and STTD P increased. A quadratic 25(OH)D3×STTD P interaction was observed for serum 1,25(OH)2D3 concentrations (P = 0.002). When pigs were fed 25(OH)D3, serum 1,25(OH)2D3 decreased (quadratic, P &lt; 0.001) as STTD P increased but the decrease was not significant when no 25(OH)D3 was fed. Added 25(OH)D3 had no effect (P &gt; 0.10) on serum 1,25(OH)2D3, but concentrations decreased (quadratic, P = 0.001) as STTD P increased. No added 25(OH)D3×STTD P interaction was observed for 24,25(OH)2D3. Serum 24,25(OH)2D3 increased (P &lt; 0.001) with added 25(OH)D3. Metacarpal bone density increased (linear, P = 0.001) as STTD P increased, as did fibulas and ribs (quadratic, P ≤ 0.055). Percentage bone ash and bone ash weight increased (quadratic, P ≤ 0.065) for all bones as STTD P increased. Added 25(OH)D3 had no effect on bone density or bone ash weight for any bones (P &gt; 0.10); however, the reduction in bone ash observed with reducing STTD P level tended to be less when 25(OH)D3 was provided (linear interaction, P = 0.098). In summary, added 25(OH)D3 had limited effect on growth performance, urine parameters, or bone characteristics; however, added 25(OH)D3 increased serum concentrations of 25(OH)D3 and 24,25(OH)2D3. Increasing STTD P to 100% of NRC requirement estimate increased growth and 130% of NRC maximized bone ash.
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