Effects Of Dietary Calcium And Non-phytate Phosphorus Levels On Growth Performance,bone Development And Related Gene Expression Of Broilers From 1 To 21 D Of Age

The present study was carried out to investigate the effects of dietary calcium(Ca)and non-phosphate phosphorus P(NPP)levels and their interactions on growth performance,bone characteristics,bone metabolism-related enzyme and proteins,and their gene expression of broilers,so as to provide a rational recommendation for Ca and NPP levels in diet.A total of 540 1-day-old Arbor Acres(AA)male broilers were randomly allotted to 1 of 15 treatments with 6 replicate cages of 6 birds per cage for each treatment.A completely randomized design involving a 5(Ca level)× 3(Npp level)two-factorial arrangement was adopted in this experiment.Dietary Ca levels were 0.60%,0.70%,0.80%,0.90% and 1.00%,and NPP levels were 0.35%,0.40% and 0.45%,respectively.The experiment lasted for 21 days.The results showed that:(1)Dietary Ca and Npp levels had no effect(P > 0.11)on average daily gain,average daily feed intake,feed/gain and mortality.The interactions between the Ca and NPP levels affected(P < 0.05)average daily gain of broilers from 1 to 21 d of age.(2)The Interactions between dietary Ca and NPP did not affect(P > 0.23)serum Ca and P concentrations and alkaline phosphatase(ALP)activity.(3)Dietary Ca level affected(P < 0.04)the bone mineral density(BMD),bone mineral content(BMC),breaking strength,ash percentage and ash Ca contents in tibia,which increased linearly as dietary Ca levels increased(P < 0.006).Dietary NPP level affected(P < 0.05)tibia BMC,ash percentage,and broilers received 0.40% and 0.45% NPP had higher(P <0.04)tibia BMC and ash percentage than those received 0.35% NPP.(4)The Interactions between dietary Ca and NPP affected(P < 0.04)ALP activity,bone glutamyl protein(BGP)and fibroblast growth factor(FGF23)contents.When the dietary NPP level was 0.40%,the tibial ALP activity in the 1.00% Ca group was significantly higher than in the other Ca level groups(P < 0.05).As dietary Ca level increased,tibia BGP content increased quadratically(P < 0.01)in chicks fed 0.35%NPP.When the dietary NPP level was 0.45%,the tibial FGF23 content in the 0.90%Ca group was lower(P < 0.05).(5)Dietary NPP level affected(P < 0.05)tibia FGF23 m RNA level,and broilers received 0.40% NPP had higher(P < 0.02)tibia FGF23 m RNA level than those received 0.35%NPP.The Interactions between dietary Ca and NPP affected(P < 0.02)tibia ALP and BGP m RNA levels.The tibia ALP m RNA was greatest(P < 0.0001)in chicks fed 1.00% Ca and 0.45% NPP diet.As dietary Ca increased,the tibia BGP m RNA increased linearly(P < 0.02)in chciks fed 0.45%NPP diet.Results from the present study indicate that when the dietary Ca and NPP levels were 0.60% and 0.35%,respectively,the broilers obtained the optimal growth performance.Dietary Ca level should be 0.90% or 1.00%,and dietary NPP level should be 0.40% or 0.45% to obtain the better bone development and related gene expression in broilers at 21 days of age.Considering all of the above indicators,the dietary levels of 0.90 % Ca and 0.45% NPP would be optimal for the overall development of broilers fed a conventional corn-soybean meal diet from 1 to 21 d of age.