Effects Of Feeding Different Doses Of 25-hydroxyvitamin D3 On Laying Performance,Egg Quality And Calcium Metabolism In Laying Hens

The objective of this study was to investigate the effects of dietary supplementation of25-hydroxyvitamin D₃（25-OH-D₃）on the laying performance,egg quality,tibia quality and calcium metabolism of characteristic laying hens in the late laying period.The appropriate addition amount of the special laying hens in the post-laying diet.Using a single-factor completely randomized experimental design,1,000 47-week-old specialty laying hens were randomly divided into 5 treatments with 5 replicates per treatment and 40 chickens per replicate.The control group was supplemented with 3,600 IU/kg of vitamin D₃ in the basal diet,and the experimental group was supplemented with 40μg/kg,65μg/kg,90μg/kg,115μg/kg of 25-OH-D₃,respectively.The pre-feeding period was 1 week and the experimental period was 6 weeks.The main test results are as follows:（1）Effects on laying performance:the addition of 65μg/kg of 25-OH-D can significantly increase the average egg weight（P<0.05）;the addition of 40μg/kg and 115μg/kg of 25-OH-D3 can significantly increase the average egg weight The proportion of sand-shell eggs was reduced（P<0.05）;different levels of 25-OH-D3 had no significant effect on the average egg production rate,feed-to-egg ratio,and average daily feed intake（P>0.05）.（2）Effects on egg quality:the addition of 65μg/kg and 90μg/kg of 25-OH-D3 can significantly increase the Hastelloy unit of eggs（P<0.05）;the addition of 65μg/kg of 25-OH-D3 The eggshell strength of the treatment group was significantly higher than that of the treatment group supplemented with 115μg/kg（P<0.05）;The shape index had no significant effect（P>0.05）.（3）Effects on tibial bone mass:the addition of 65μg/kg and 90μg/kg of 25-OH-D3 can significantly increase the tibial bone density（P<0.05）;the addition of 65μg/kg of 25-OH-D3 can significantly improve Tibial strength and defatted dry weight of tibia（P<0.05）;different levels of 25-OH-D3 had no significant effect on tibia fresh weight and ash（P>0.05）.（4）Effects on bone synthesis and bone resorption:In terms of bone synthesis,the addition of 90μg/kg of 25-OH-D3 can significantly increase the content of bone-derived alkaline phosphatase,osteocalcin and osteoprotegerin in serum（P<0.05）;in terms of bone resorption,the addition of 65μg/kg and 90μg/kg of 25-OH-D3 can significantly reduce the content of tartrate-resistant acid phosphatase in serum,and the addition of 90μg/kg of 25-OH-D3 can significantly reduce the content of tartrate-resistant acid phosphatase in serum.The content of type I collagen C-terminal peptide was significantly reduced,and different levels of 25-OH-D3 had no significant effect on osteopontin content（P>0.05）.（5）Effects on calcium metabolism:adding 65μg/kg and 90μg/kg 25-OH-D3 could significantly increase serum 1,25-（OH）2-D3 content（P<0.05）;adding 90μg/kg kg of 25-OH-D3 can significantly increase the content of calcitonin in serum（P<0.05）;different levels of 25-OH-D3 have no significant effect on serum phosphorus,serum calcium,alkaline phosphatase and parathyroid hormone（P>0.05）.（6）Effects on the expression of calcium metabolism-related genes in various tissues:in the determination of relative gene expression in duodenal tissue,the addition of 90μg/kg and115μg/kg of 25-OH-D3 could significantly increase the expression of calcium metabolism-related genes.The m RNA expressions of Ca BP-D_28k and NCX were increased（P<0.05）;the expression of VDR was significantly increased in all treatment groups（P<0.05）,and the treatment group added 40μg/kg had the highest expression（P<0.05）;The addition of 40μg/kg,90μg/kg and 115μg/kg of 25-OH-D3 significantly increased the expression of PMCA（P<0.05）.In the determination of gene relative expression in kidney tissue,the addition of40μg/kg,65μg/kg and 90μg/kg of 25-OH-D3 significantly increased the m RNA expression of CYP₂₇B₁（P<0.05）;the addition of 65μg/kg and 90μg/kg of 25-OH-D3 could significantly increase the expression of Ca BP-D_28k（P<0.05）.In the determination of relative gene expression in uterus,the addition of 90μg/kg 25-OH-D3 significantly increased the relative m RNA expression of NCX（P<0.05）;the addition of 65μg/kg 25-OH-D3significantly increased the expression of ERαExpression level（P<0.05）.In conclusion,different levels of 25-OH-D3 have different effects on all aspects of characteristic laying hens.Among them,65μg/kg level of 25-OH-D3 has the most obvious effect on all aspects,and has the most obvious effect on laying performance,egg quality,tibia quality,Calcium and phosphorus metabolism hormones and some indicators of candidate gene expression had significant effects,and the comprehensive effect was the best.