Growth performance, bone mineralization, and mineral transporter gene expression in broiler chickens fed varying non-phytate phosphorus levels at a fixed calcium to non-phytate phosphorus ratio

This study investigated the effects of dietary non-phytate phosphorus (NPP) levels on growth performance, bone mineralization, and mineral transporting gene expression in broilers (1-21 d), under a 2:1 calcium (Ca)-to-NPP ratio. The six Ca:NPP levels were 0.90 %:0.45 %, 0.80 %:0.40 %, 0.70 %:0.35 %, 0.60 %:0.30 %, 0.50 %:0.25 %, and 0.40 %:0.20 %, respectively. A total of 360 male broilers (day 1) were randomly assigned to 6 groups (5 cages per group, 12 birds per cage). Feed intake and weight gain (WG) were not affected by reductions in NPP from 0.45 % to 0.25 % (at a 2:1 Ca-to-NPP ratio) (P > 0.05), but WG was reduced in birds receiving 0.20 % NPP relative to those receiving 0.45 % NPP (P < 0.05). Femur and tibia quality were not altered by decreasing NPP from 0.45 % to 0.40 %, but further reduction to 0.20 % resulted in declines in bone weight and phosphorus (P) content (P < 0.05). Transcription of duodenal P transporter genes (NaPi-IIb and PiT-1), Ca transporter genes (NCX1, PMCA1b, and CaBP-D28k), as well as renal NaPi-IIa and CaBP-D28k, were upregulated in response to reduced dietary NPP and Ca levels (P < 0.05). In the duodenum, PiT-1 and NaPi-IIb transcription levels were elevated in birds receiving 0.20 %-0.40 % NPP relative to those receiving 0.45 % NPP (P < 0.05). Similarly, NCX1, PMCA1b, and CaBP-D28k transcription levels were increased in birds fed 0.40 %-0.50 % Ca relative to those fed 0.90 % Ca (P < 0.05). In the kidney, NaPi-IIa transcription levels were higher in birds fed 0.20 %-0.25 % NPP than in those receiving 0.45 % NPP (P < 0.05), whereas CaBP-D28k expression increased in birds receiving 0.40 %-0.60 % Ca relative to those receiving 0.90 % Ca (P < 0.05). These findings suggest that, under a constant Ca:NPP ratio of 2:1, moderate reductions in Ca and NPP do not impair growth performance of broilers (1-21 d) and may enhance mineral absorption via transcriptional up-regulation of transporter genes in the intestine and kidney.