Intestinal segment and vitamin D3 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<sub>3</sub> (VD<sub>3</sub>) concentration (0, 125, 250, 500, 1000, and 2000 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<sub>3</sub>. 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<sub>3</sub> 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 (<italic>p</italic> < 0.05). The rise in dietary VD<sub>3</sub> levels from 125 to 1000 IU/kg further increased the BWG, FI, and weights of the bone, ash, Ca, and P (<italic>p</italic> < 0.05). No difference in growth rate and leg bone quality was noted in the broilers provided with 1000 and 2000 IU/kg VD<sub>3</sub> (<italic>p</italic> > 0.05). Supplementation with 125–2000 IU/kg VD<sub>3</sub> increased the mRNA abundances of intestinal Ca and P transporters to varying degrees. The mRNA level of CaBP-D28k increased by 536, 1161, and 28 folds in the duodenum, jejunum, and ileum, respectively, after adding 1000 IU/kg VD<sub>3</sub>. 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 1000–2000 IU/kg VD<sub>3</sub>. These data suggest that intestinal Ca and P transporters are mainly expressed in the duodenum of broilers. Moreover, the addition of VD<sub>3</sub> stimulates the two mineral transporter transcription in broiler intestines.