Effects Of Dietary Phosphorus Levels On Laying Performance、Egg Shell Quality And Ca And P Absorption In Laying Hens With Drawf Gene

In order to systemically investigate the effect of different levels of dietary phosphorus on the production performance, metabolism of calcium and phosphorus and immunity stress in layers, and determine phosphorus supply in the dwarf layers of dietaryExperiment1:The corn-soybean meal with5levels of non-phytate phosphorus (NPP) were used. A total of405pink-shell dwarf layers aged at28weeks were randomly divided into9treatments with9replicates each. Production performance at and after peak production, egg quality and expression of genes related to calcium and phosphorus were investigated. Dietary NPP of0.3%could meet the requirement for the peak egg production (30-40weeks of age), while NPP of0.2%was sufficient for the production performance of layers aged at50-61weeks. With the increment in dietary NPP, the ConA stimulation index displayed a quadratic relationship with the highest level at0.28%of dietary NPP. At41weeks of age, with the increase in dietary NPP, the Nap Ⅱb mRNA abundance in duodenum decreased linearly, while kidney Nap Ⅱa mRNA increased linearly. The levels of CaBP mRNA and protein expression showed a quadratic relationship with dietary NPP with highest expression at the0.25%and0.30%of NPP, respectively. Those results suggested that the requirement of NPP decreased, but calcium requirement increased in aged birds. In accordance, the expression of Nap Ⅱb mRNA and CaBP mRNA decreased and increased in the duodenum.Experiment2:The2*3factorial experimental design was adopted with2levels of multi-vitamin supplements and3levels of dietary NPP (0.2%,0.3%and0.4%) in the corn-soybean meal. A total of450layers has been randomly divided to5treatments with5repeats each treatment of15birds each. Egg production and egg quality were investigated. Highest egg production was observed when0.3%of NPP were supplemented in the diet containing low level of multi-vitamin. The eggshell color was darken with the increment in dietary NPP and multi-vitamin. Dietary NPP significantly increased serum phosphorus but decreased serum calcium content. Multi-vitamin supplements increased the serum albumin and decreased serum ALP. There were interactions on serum phosphorus and T-SOD activity between dietary NPP and multi-vitamin. Compared with unspotted eggs, the thickness of eggshell and the membrane was thinner in spotted eggs. The contents of phosphorus and calcium were lowered in the inner membrane and the outer membrane of spotted eggshell, respectively. In layers producing spotted eggs, uterus CaBP mRNA and Ca2+-ATPase mRNA expression was lower than normal hens; in contrast, serum MDA was higher. The results suggested calcium and phosphorus metabolism closely related with the formation of spotted eggs. The eggshell and membrane thickness positively correlated with the spots formation and the effective thickness of papillary layer has a determinative role in eggshell quality. Dietary NPP of0.4%decreased the ratio of spotted eggs.Experiment3:The layer were fed either0.12%or0.4%dietary NPP in corn-soybean meal. A total of300healthy layers aged28weeks old has been randomly divided to2dietary treatment groups with10repeats each treatment of15birds each. All bird were prefed for4weeks and the trial lasted for5weeks. At the age of32weeks, half birds of each dietary treatment received LPS or saline administration ip on every the other day for9days. Egg production and egg quality were determined when immunologically stressed those layers. Administration of LPS elevated the rectal temperature after3hours and significantly decreased feed intake and egg production. LPS-induced immune stress significantly increased eggshell thickness, strength, albumin height and Haugh unit. There was a significant interaction between dietary NPP and LPS treatment. LPS-induced immune stress lowered serum calcium, phosphorus, total protein, albumin, globulin and SOD activities, but increased MDA, IL-1β and IL-6in the serum. Layers received LPS had higher relative weight of liver and spleen than those received saline. LPS stimulation significantly increased cecum IL-1β, IL-6and IL-10mRNA expression. LPS administration also damaged the architecture of intestine villi, decreased the ratio of villi height/crypt depth and dampened the crypt. Dietary phosphorus significantly increased the ratio of villi height/crypt depth, decreased serum MDA and IFN-y and alleviated the damage in the intestine.In conclusion, the recommended dietary NPP for pink-shell dwarf layers were0.3%and0.2%at the peak production and after the peak production, respectively. The requirement for NPP and calcium decreased and increased in aged layers, respectively. The CaBP mRNA abundance in the uterus was lower in birds producing spotted eggs than normal birds, indicating the close relationship between the formation of spotted eggshell and metabolism of calcium and phosphorus. The eggshell and membrane thickness positively correlated with the spots formation. LPS-induced immune stress significantly decreased egg production and damaged the architecture of intestine villi and high level of dietary NPP could alleviate the damage by elevating serum IFN-y.