| This study was conducted to investigate the effect of dietary non-phytate phosphorus(NPP) level on growth performance of broilers from 1 to 21 d of age, phosphorus(P) contents in plasma from portal vein blood, as well as mRNA and protein expression levels of type IIb sodium-dependent phosphate cotransporter(NaP-IIb), inorganic phosphate transporter 1(PiT-1) and inorganic phosphate transporter 2(PiT-2) in the small intestinal segments(duodenum, jejunum, and ileum) of broilers at 7, 14 and 21 d of age, so as to elucidate the molecular mechanisms of P absorption.A total of 450 1-d-old commercial Arbor Acres(AA) male broilers were randomly allocated to 3 treatments by bodyweight, with 10 replicate cages of 15 chicks per cage for each treatment. The birds were fed a basal corn-soybean meal diet(containing 0.06% NPP by analysis), or the basal diet supplemented with normal NPP level(containing 0.44% NPP by analysis) according to the NPP recommendation of NRC(1994), or the diet supplemented with half of the recommended NPP level(containing 0.21% NPP by analysis). The diets were supplemented with inorganic P in the form of CaHPO4?H2O, and in order to eliminate the effect of calcium(Ca) on the P absorption, all diets contained the same amount of Ca(1.0%). The experiment lasted for 21 d. The results indicated that(1) dietary NPP level significantly affected the average daily gain(ADG), average daily feed intake(ADFI), mortality and feed/gain(F/G)(P < 0.0001). The ADG and ADFI increased but the F/G decreased linearly as dietary NPP level increased.(2) Dietary NPP level significantly affected the P contents in plasma from portal vein blood at 7, 14 and 21 d of age(P < 0.0001), and the plasma P contents in 0.44% NPP level group were significantly higher than those in 0.21% NPP level and control groups(P < 0.0012). Besides, the plasma P contents in 0.21% NPP level group were higher than that in 0.06% NPP level group at 7 and 14 d of age(P < 0.0001), but no significant difference was found in plasma P contents of broilers at 21 d of age between the 2 groups(P > 0.60).(3) Dietary NPP level significantly affected the mRNA expressions of NaP-IIb(P < 0.012), PiT-1(P < 0.038) and PiT-2(P < 0.029) in the duodenum of broilers at 14 d of age, and affected the mRNA expressions of NaP-IIb(P < 0.0002), PiT-1(P < 0.011) and PiT-2(P < 0.003) in the duodenum of broilers at 21 d of age. Compared with the control group, the broilers at 14 and 21 d of age fed 0.44% NPP level diet had lower(P < 0.002) duodenal NaP-IIb and PiT-1 mRNA levels while higher(P < 0.014) PiT-2 mRNA level. The NaP-IIb mRNA was mainly expressed in the duodenum, but PiT-1 and PiT-2 mRNA was mainly expressed in the ileum.(4) Dietary NPP level significantly affected the protein expressions of NaP-IIb(P < 0.0024), PiT-1(P < 0.0007) and PiT-2(P < 0.0001) in the duodenum of broilers at 14 d of age, and affected the protein expressions of NaP-IIb(P < 0.0003), PiT-1(P < 0.0007) and PiT-2(P < 0.037) in the duodenum of broilers at 21 d of age. Compared with the control group, the NaP-IIb(P < 0.0006) and PiT-2(P < 0.014) protein expression levels were significantly higher while the PiT-1(P < 0.0002) protein expression level was significantly lower in the 0.44% NPP level group. In conclusion, dietary NPP level significantly affected the growth performance, P contents in plasma from portal vein blood, the mRNA and protein expression levels of small intestinal NaP-IIb, PiT-1 and PiT-2 of broilers. The diet supplemented with proper NPP level might increase the ADG, ADFI, but decrease the mortality and F/G, as well as promote the P absorption in the small intestine of broilers by increasing the NaP-IIb and PiT-2 protein expression levels while decreasing the PiT-1 protein expression level. |
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