| Calcium(Ca)and phosphorus(P)are important mineral elements for bone development of poultry,and Ca and P deficiency could lead to abnormal bone development,such as rickets.The rickets of broilers at different days of age might have different sensitivities to Ca or P deficiency.The regulatory mechanism of Ca on bone development has been reported in previous studies,but it is unclear how P regulates bone development of broilers.Therefore,the present study was to investigate that effects of dietary Ca and P deficiency on tibia histological structure of broilers at grower phases,and the changing patterns and correlations of bone P retention and development of broilers at whole phases.It will be great theoretical and practical significances for how to identity and prevent the rickets induced by Ca or P deficiency of broilers in the early stage,and how to improve dietary P utilization efficiency and minimize the environmental pollution of P excreted by broilers.Experiment 1 was conducted to investigate the effects of dietary Ca and P deficiency on growth performance,the characters of rickets incidence and tibia histological structure.A completely randomized design with a 2[dietary Ca contents:1.00%and 0.35%]× 2(dietary non-phytate P(NPP)contents:0.45%and 0.23%)factorial arrangement.A total of 504 one-d-old AA male broilers were assigned randomly into 4 treatments with 7 replicate cages of 18 broilers per cage for each treatment.The experiment lasted for 21 d.The results showed that the interaction between Ca level and NPP level was significant(P<0.05)for the growth performance of broilers at different grower phases and the lengths of proliferating zone and hypertrophy zone in the tibia growth plate at days 7 or 14.When broilers were fed diet containing 1.00%Ca,low level of NPP decreased(P<0.05)average daily feed intake(ADFI)and average daily gain(ADG)at different grower phases,bLut increased(P<0.05)the radio of feed:gain(F/G)and the length of hypertrophy zone in the tibia growth plate at day’s 7 or 14.When broilers were fed diet containing 0.35%Ca,low level of NPP increased(P<0.05)the ADG of broilers during 15 to 21 or 1 to 21 days of age and the length of hypertrophy zone in the tibia growth plate at days 7,but lowered(P<0.05)the length of proliferating zone in the tibia growth plate at days 7.Besides,compared with the diet containing 1.00%Ca and 0.23%NPP,the diets containing 0.35%Ca and 0.45%NPP or the diet containing 0.35%Ca and 0.23%NPP increased(P<0.05)ADFI and ADG at all grower phases,but reduced(P<0.05)the length of hypertrophy zone in the tibia growth plate at days 7 or 14.The results indicate that the growth performance and rickets incidence are the most sensitive to the NPP deficient diet,followed by the Ca deficient diet,and then the Ca-NPP deficient diet.The different tibia histological structures show that the hypertrophy zone in the tibia growth plate is lengthenecd in the NPP deficiency,while the proliferating zone is lengthened in the Ca deficiency and Ca-NPP deficiency,but Ca-NPP deficiency has the shorter proliferating zone than Ca deficiency in the early stage.Based on the results of experiment 1 that the rickets incidence of broilers was the most sensitive to the NPP deficient diet,experiment 2 was carried out to investigate the tibia P retention and development as well as their correlations and possible mechanisms of broilers at different days of age.A total of 320 one-d-old AA male broilers were raised in 8 replicate cages of 40 birds per cage,and fed the same corn-soybean diets for 42 d.Plasma and tibia samples of broilers were collected on d 1,7,14,21,28,35 or 42.The results showed that the tibia ash P content increased linearly(P=0.017),and the total P accumulation in tibia ash increased linearly and quadratically(P<0.001)with age.The traits of bone development,including the tibia bone mineral content(BMC),the tibia bone mineral density(BMD)and the tibia ash content increased linearly and quadratically(P<0.001),while the tibia breaking strength increased linearly(P<0.001)with age.The tibia bone gal protein(BGP)content decreased linearly(P=0.011),but neither a linear nor quadratic(P>0.15)response was observed for the tibia alkaline phosphatase(ALP)with age.The tibia ash P content was positively correlated with the tibia BMD(r=0.325,P=0.014),ash(r=0.325,P=0.001)and ALP(r=0.377,P=0.004).The total P accumulation in tibia ash also was positively correlated with all of the above traits of bone development(r=0.437-0.976,P<0.001),however,it was negatively correlated with the tibia BGP(r=-0.426,P=0.0014).Additionally,the tibia ALP was positively correlated with the tibia ash(r=0.369,P<0.001),and the tibia BGP was negatively correlated xwith the tibia BMC(r=-0.453,P<0.001),breaking strength(r=-0.384.P<0.001)and ash content(r=-0.361,P<0.001).The above results indicated that the bone P retention was involved in the bone development of broilers from 1 to 42 d of age possibly via the regulation of the bone ALP and BGP.The above two experiments revealed that tibia histological structures were the most sensitive to the NPP deficient diet,followed by the Ca deficient diet,and then the Ca-NPP deficient diet;bone P retention was involved in the bone development of broilers at different days of age possibly via the regulation of the bone ALP and BGP. |
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