Study On The Expression Changes Of The Factors Related To Calcium-phosphorus Metabolism In The Duodenum And Kidney Of The Osteoporosis Laying Hens

Cage layer osteoporosis(CLO)is one of the most frequent diseases in cage laying hens.At present,most scholars believe that the disease is caused by the metabolic unbalance of calcium and phosphorus in the layers.The process of calcium and phosphorus metabolism in layers is regulated by duodenum,kidney,eggshell gland and bone.In the late stage of laying,the laying hens need to replenish large amounts of calcium to meet the needs of laying eggs.Otherwise,bone calcium will be used.But until now,the exact mechanism of CLO is not clear.In this experiment,the CLO model was induced to detect the factors related to calcium and phosphorus metabolism in the blood,duodenum and kidney of CLO model,bone biological index and the changes of renal histomorphology,in order to discover the rules and reveal the pathogenesis of CLO,and provide a theoretical basis for the prevention and therapy of CLO in production.Hyland brown commercial laying hens(216 at 73 weeks of age)were used as experimental animals,and low calcium diet was used to induce CLO model,serum calcium and phosphorus metabolism related biochemical indicators,bone index,bone density,tibia three point bending load and maximum stress were measured by conventional methods.Micro-ct scan of the tibia and TRAP staining of the tibia were used to observe the morphological changes of bone tissue.Real time PCR was used to detect the mRNA expression levels of calcium and phosphorus metabolism-related factors in the duodenum and kidney.HE staining and electron microscope were used to observe the morphological changes of kidney tissue.The results showed that: 1.The CLO model was successfully induced in this experiment.When CLO occurred,the content of serum Ca and P decreased;the actrivity of alkaline phosphatase(ALP)and tartrate acid phosphatase(TRAP)increased;the bone biomechanics index decreased;cortical bone and medullary osteolysis,osteoclast(OC)increased,and the tibial cortical bone was partially altered.The number of trabecular bones in the medullary bone is smaller and the volume is smaller than the control hens.2.The expression levels of duodenal calcium binding protein(CaBP-D28k)and vitamin D receptor(VDR)mRNA was significantly up-regulated in osteoporotic layers,and the expression level of sodium and phosphorus co transporter 2b(NaPi-IIb)mRNA decreased significantly.With the CLO exacerbation,the serous calcium ATP enzyme(PMCA1b)mRNA expression lelvel was first upregulation and then downregulation,however NCX1 mRNA ecpressen level had opposite changes.The results indicated that duodenal calcium absorption capacity increased and phosphorus uptake capacity decreased after CLO.3.24-hydroxylase(Cyp24al),calcium channel instantaneous receptor potential vanillin receptor 5(TRPV5),calcium channel transient receptor 6(TRPV6),NCX1,and sodium phosphorus co transporter 2a(NaPi-IIa)mRNA expression levels were significantly downregulated,yet parathyroid hormone receptor(PTHR),CaBP-D28 K,PMCA1b,fibroblast growth factor receptor 1(FGFR1),fibroblast growth factor receptor 3(FGFR3),fibroblast growth factor receptor 4(FGFR4)and Klotho mRNA expression levels were up-regulated,indicating that the renal calcium and phosphorus reabsorption and excretion ability of the kidney are enhanced,and the absorption capacity of phosphorus is weakened.4.We also found that the renal structure was destroyed when CLO happened,the symptom was as follows,the rupture of the renal tubule wall layer in the osteoporotic layer,the vacuolation of the cytoplasm of the renal tubular epithelial cells,the exudation in the renal tubules,the rupture of mitochondria,the enlargement of mitochondria,and the dissolving or breaking of the crista.This experimental results showed that: when laying hens occurred CLO,the bone remodeling activity was active,but the osteoclast activity was stronger than the osteogenic activity,the bone biological index was lower,the absorption / reabsorption capacity of the duodenum and kidney to calcium was enhanced,the absorption ability of the duodenum and kidney to phosphorus was weakened,and the excretion ability of the kidney to phosphorus was enhanced.