Study On Dietary Non-phytate Phosphorus Requirement Of Broiler Chicks From22to42Days Of Age

The main objective of this study was to determine the non-phytate phosphorus (NPP) requirementfor broiler chicks from22to42days of age by investigating the effect of dietary NPP levels onperformance, carcass traits, meat quality, bone mineral content (BMC), bone mineral density (BMD),body bone mineral content, body bone mineral density and tissue gene expression of NaPi-Ⅱa mRNA,NaPi-Ⅱb mRNA and AKP mRNA of broilers. A total of500commercial1-d-old Arbor Acres malebroilers were housed in electrically heated, stainless steel suspended cages with fiberglass feeder andwater troughs. Birds were allowed ad libitum access to diets and tap water, and maintained on a24-hconstant-light schedule. All birds were fed the same corn-soybean meal diet containing0.39%NPP byanalysis from1to21days of age. At22days of ages,360birds were selected and randomly allotted bybody weight to one of10treatments of6replicate cages (6chicks per cage) in a completely randomlydesign, and fed the P-unsupplemented basal corn-soybean meal diet or the basal diet supplemented with0.05,0.10,0.15,0.20,0.25,0.30,0.35,0.40or0.45%inorganic phosphorus in the form of CaHPO4(feed-grade), respectively. The dietary NPP concentrations by analysis on as-fed basis were0.09,0.14,0.20,0.24,0.30,0.34,0.38,0.45,0.49and0.54%, respectively. Metabolizable energy, crude protein,and Ca concentration etc. in all treatment diet were similar. The results showed that carcass traits, meatquality, serum PTH, serum Ca concentration, ash Ca concentrain, bone marrow AKP activity were notaffected(P＞0.05) by dietary NPP levels, but average daily gain(P＜0.0001), average feed intake(P＜0.0001), serum inorganic P(P＜0.0001), serum AKP activity(P＜0.05), bone characteristics(P＜0.0001), and gene expression of NaP-IIb mRNA(P＜0.0001), NaP-IIa mRNA(P＜0.0001), and bonemarrow AKP mRNA(P＜0.05) were affected by dietary NPP level. Serum inorganic P, tibia ashpercentage, tibia ash P concentration, tibia bone strength, tibia BMC, tibia BMD, body bone mineraldensity, and middle toe ash percentage were the sensitive indices of estimating NPP requirement ofbroilers from22to42days of age, while body BMD, tibia BMC and BMD were new and specificlysensitive criteria for estimating optimal NPP requirement of broiler chicks. According to the abovesensitive indices, the estimated NPP requirements of broiler chicks from22to42days of age were0.29、0.29、0.29、0.29、0.31、0.31、0.28,0.30and0.27%. Based on all the above results, the dietary NPPrequirement was0.31%for broiler chicks from22to42days of age fed a corn-soybean meal diet.