Dietary vitamin D supplementation does not affect Na+ ‐dependent phosphate uptake and expression of NaPi‐IIb cotransporter in the small intestine of vitamin D deficient weanling pigs

The objective of this experiment was to determine if dietary vitamin D supplementation to vitamin D deficient pigs affects Na + ‐dependent nutrient uptake and mRNA expression of NaPi‐IIb and calbindin D(9k) in the jejunum. Pigs (n=32) were removed from sows at 2 d of age and placed on a vitamin D deficient liquid diet in a room devoid of sunlight and UV light in the range of 280–300nm. On d 28, serum 25(OH)D 3 (μ=14.67 ± 0.47 nmol/L) and Ca concentrations (μ=9.78 ± 0.29 mg/dL) were measured to verify vitamin D deficiency status. Pigs (10.18 ± 0.38 kg) were then fed diets supplemented with: 0, 220, or 1500 IU/kg diet of vitamin D for 12 d. Jejunal segments were mounted in Ussing chambers and Na + ‐dependent phosphate and glucose transport did not differ (P>0.10) among treatment groups. NaPi‐IIb and calbindin D(9k) (real‐time PCR) mRNA expression were not different (P>0.10) between treatment groups. Final serum Ca concentrations (P<0.001) were 11 and 5% greater for pigs fed the 1500 IU/kg diet compared to pigs fed the 220 and 0 IU/kg diets, respectively. However, no differences were detected in final serum P or 25(OH)D 3 concentrations. Serum Ca and 25(OH)D 3 increased (P<0.001) and serum P tended (P<0.10) to increase from d 28 to d 40. Overall, jejunal Na + ‐dependent phosphate uptake and NaPi‐IIb mRNA expression were not stimulated by feeding increasing concentrations of vitamin D to piglets with a 25(OH)D 3 status of <25 nmol/L.