Abstract
1,25-Dihydroxycholecalciferol (1,25-(OH)(2)-D(3)) is the final active product of vitamin D. This study aimed to investigate the effects of 1,25-(OH)(2)-D(3) on growth performance, bone development, and calcium (Ca) transporter gene expression levels in the small intestine of broiler chickens. On the day of hatching, 140 female Ross 308 broilers were randomly allotted into two treatments with five replicates (14 birds per replicate). Two levels of 1,25-(OH)(2)-D(3) (0 and 1.25 µg/kg) were added to the basal diet without vitamin D. Results showed that the addition of 1.25 µg/kg 1,25-(OH)(2)-D(3) increased the average daily feed intake and the average daily gain and decreased the feed conversion ratio and mortality in 1- to 19-day-old broiler chickens compared with the basal diet without vitamin D (P<0.05). 1,25-(OH)(2)-D(3) also enhanced the length, weight, ash weight, and the percentage contents of ash, Ca, and P in the tibia and femur of broilers (P<0.05). The mRNA expression levels of the Ca-binding protein (CaBP-D28k) in the duodenum, jejunum, and ileum of 19-day-old broilers increased to 88.1-, 109.1-, and 2.7-fold, respectively, after adding 1,25-(OH)(2)-D(3) (P<0.05). The mRNA expression levels of the plasma membrane Ca ATPase 1b (PMCAlb) in the duodenum and the sodium (Na)/ Ca exchanger 1 (NCX1) in the duodenum and the jejunum were also enhanced to 1.57-2.86 times with the addition of 1,25-(OH)(2)-D(3) (P<0.05). In contrast, the mRNA expression levels of PMCA1b and NCX1 in the ileum and that of vitamin D receptor (VDR) in the small intestine were not affected by 1,25-(OH)(2)-D(3) (P>0.05). These data indicate that 1,25-(OH)(2)-D(3) upregulated Ca transporter gene transcription and promoted Ca(2+) absorption in the small intestine, especially in the proximal intestine (duodenum and jejunum), thereby improving growth performance and bone mineralization in broiler chickens.