Intestinal segment and vitamin D 3 concentration affect gene expression levels of calcium and phosphorus transporters in broiler chickens.

Two experiments were conducted in this research. Experiment 1 investigated the spatial expression characteristics of calcium (Ca) and phosphorus (P) transporters in the duodenum, jejunum, and ileum of 21-day-old broilers provided with adequate nutrient feed. Experiment 2 evaluated the effects of dietary vitamin D 3 (VD 3 ) concentration (0, 125, 250, 500, 1,000, and 2,000 IU/kg) on growth performance, bone development, and gene expression levels of intestinal Ca and P transporters in 1-21-day-old broilers provided with the negative control diet without supplemental VD 3 . Results in experiment 1 showed that the mRNA levels of calcium-binding protein 28-kDa (CaBP-D28k), sodium-calcium exchanger 1 (NCX1), plasma membrane calcium ATPase 1b (PMCA1b), and IIb sodium-phosphate cotransporter (NaPi-IIb) were the highest in the broiler duodenum. By contrast, the mRNA levels of inorganic phosphate transporter 1 (PiT-1) and 2 (PiT-2) were the highest in the ileum. Results in experiment 2 showed that adding 125 IU/kg VD 3 increased body weight gain (BWG), feed intake (FI), bone weight, and percentage and weight of Ca and P in the tibia and femur of 1-21-day-old broilers compared with the negative control diet ( p < 0.05). The rise in dietary VD 3 levels from 125 to 1,000 IU/kg further increased the BWG, FI, and weights of the bone, ash, Ca, and P ( p < 0.05). No difference in growth rate and leg bone quality was noted in the broilers provided with 1,000 and 2,000 IU/kg VD 3 ( p > 0.05). Supplementation with 125-2,000 IU/kg VD 3 increased the mRNA abundances of intestinal Ca and P transporters to varying degrees. The mRNA level of CaBP-D28k increased by 536, 1,161, and 28 folds in the duodenum, jejunum, and ileum, respectively, after adding 1,000 IU/kg VD 3 . The mRNA levels of other Ca and P transporters (PMCA1b, NCX1, NaPi-IIb, PiT-1, and PiT-2) increased by 0.57-1.74 folds by adding 1,000-2,000 IU/kg VD 3 . These data suggest that intestinal Ca and P transporters are mainly expressed in the duodenum of broilers. Moreover, the addition of VD 3 stimulates the two mineral transporter transcription in broiler intestines.