Effects Of 1α-hydroxycholecalciferol On Growth Performance,Bone Mineralization,Plasma Biochemical Parameters,and MRNA Of Sodium-dependent Phosphate Cotransporter In Small Intestine Of Broiler Chickens

The relative bioavailability（RBV）of 1α-hydroxycholecalciferol（1α-OH-D₃）to cholecalciferol（VD₃）and the effects of of 1α-OH-D₃ levels on growth performance,bone mineralization,and mRNA expression of 25-hydroxylase in liver and sodium phosphate cotransporter in small intestine and kidney in 1-to 21-d-old broiler chicks fed with calcium（Ca）-and phosphorus（P）-deficient diets were studied in our research.This study aims to discuss whether 1α-OH-D₃ promote the absorption of inorganic phosphorus（Pi）,which relates to the decrease of dietary phosphorus levels,and reducing environmental phosphorus pollution.Experiment 1 Comparison of Bioavailability of 1α-Hydroxycholecalciferol and Cholecalciferol in Broiler Chicken DietsThe 400 male of 1-d-old Ross 308 broilers used in the experiment were weighted at 1 d,and all had a similar weight.All chicks were randomly assigned to 8 treatments with 5 replicates each.Eight test diets were designed in this study.Five levels of D₃（0,2.5,5,10,and 20 μg/kg）and three levels of 1α-OH-D₃（1.25,2.5,and 5 μg/kg）were added to a basal diet.The basal diet contained 0.50% Ca and 0.25% non-phytate phosphorus（NPP）,without D₃.The relative bioavailability（RBV）of 1α-OH-D₃ to D₃ was determined by the slope ratio method.Results as follows:（1）1α-OH-D₃ or VD₃ linearly increased body weight gain（BWG）,feed intake（FI）,plasma Ca（P<0.05）;the weight,length,width,ash weight and content,and Ca and P content of tibia,femur and metatarsus responded linearly to 1α-OH-D₃ or VD₃ levels（P<0.05）.（2）Using body weight gain,feed intake,and plasma Ca as criteria,the RBV of 1α-OH-D₃ to D₃ were 4.78,4.75,and 4.21,respectively.Using tibia weight,length,width,ash weight and content,and Ca and P content as criteria,the RBV of 1α-OH-D₃ to D₃ were 5.58,5.16,4.42,4.70,5.03,4.46,4.70,and 4.79.Using femur weight,length,width,ash weight and content,and Ca and P content as criteria,the RBV of 1α-OH-D₃ to D₃ were 5.09,4.43,3.19,5.83,5.21,5.27,and 5.31.Using metatarsus weight,length,width,ash weight,and Ca content as criteria,the RBV of 1α-OH-D₃ to D₃ were 5.00,4.05,5.94,4.73,and 5.64.These data indicate that the RBV of 1α-OH-D₃ to D₃ is 4.83 in promoting growth performance and bone mineralization in broilers from 1 to 21 d of age.（3）These data indicate that the RBV of 1α-OH-D₃ to D₃ is 4.83 in promoting growth performance and bone mineralization in broilers from 1 to 21 d of age.Experiment 2 Influence of the Levels of 1α-Hydroxycholecalciferol on Growth,Bone Mineralization,and mRNA Expression of Sodium Phosphate Cotransporter in Small Intestine of ChicksThe 250 male of 1-d-old Ross 308 broilers used in the experiment were weighted at 1 d,and all had a similar weight.All chicks were randomly assigned to 5 treatments with 5 replicates each.A basal diet（Table 1）was formulated to contain suboptimal concentrations of Ca（0.50%）and NPP（0.25%）,without D₃.Four levels of 1α-OH-D₃（0,1.25,2.5,and 5 μg/kg）were added to the basal diet.Meanwhile,the positive control was designed containing 1.00% Ca,0.45% NPP,and 25 μg/kg vitamin D₃.The date of performance was recorded during the 21-d experiment.on day 21,a chicken weighing close to the average weight of the replicate was selected and killed for collection of blood,bones,tissues of liver,kidney,and small intestine.Primer sets were designed using software（Primer Premier 5.0）for the examination of gene expression by Real-time PCR.Results as follows:（1）The levels of 1α-OH-D₃（0,1.25,2.5 and 5 μg/kg）improved BWG,FI,feed efficiency（FE）,utilization and retention of Ca and t P of broilers from 1 to 21 days of age（P<0.05）;broilers fed with basal diets supplemented with 5 μg/kg 1α-OH-D₃ exhibited equal growth performance compared with the birds fed with control diets（P>0.05）.（2）The levels of 1α-OH-D₃（0,1.25,2.5 and 5 μg/kg）increased plasma Ca and Pi（P<0.05）,decreased plasma alanine aminotransferase（ALT）,aspartate aminotransferase（AST）,lactate dehydrogenase（LDH）,creatinine（CRE）,and total protein（TP）（P<0.05）of broilers.（3）The levels of 1α-OH-D₃（0,1.25,2.5 and 5 μg/kg）increased the tibia and femur weight,length,width,ash weight and content,and Ca and P content of broilers（P<0.05）;the tibia and femur in birds fed the basal diet supplemented with 5 μg/kg 1α-OH-D₃ were able to achieve the same weight and ash content values as chicks fed the control diets（P>0.05）.（4）The levels of 1α-OH-D₃（0,1.25,2.5 and 5 μg/kg）up-regulate the mRNA expression of 25-hydroxylase in liver and nuclear vitamin D receptor（n VDR）,type Ⅱb sodium phosphate cotransporter（Na Pi-Ⅱb）,protein kinase C（PKCα and PKCβ）in small intestine（P<0.05）.The levels of 1α-OH-D₃ increased kidney n VDR mRNA levels（P<0.05）,and there was a trend for increasing the mRNA expression of type Ⅱa sodium phosphate cotransporter（Na Pi-Ⅱa）and type Ⅱc sodium phosphate cotransporter（Na Pi-Ⅱc）in kidney.No significant differences were observed in the mRNA expression of 25-hydroxylase,n VDR,Na Pi-Ⅱa,Na Pi-Ⅱb,Na Pi-Ⅱc,PKCα and PKCβ between the birds fed 5 μg/kg 1α-OH-D₃ and the birds fed the control diets.