Effects Of Dietary Non-Phytate Phosphorus Levels On Laying Performance And Phosphorus Metabolism In Laying Hens

Phosphorus is an essential mineral element in the life of laying hens.There is a positive effect on maintaining the health of laying hens,reducing feed costs and mitigating environmental pollution with suitable phosphorus levels.However,the level of non-phytate phosphorus?nPP?in Chinese chicken laying stocks is generally high,and the utilization rate of laying hens is low,resulting in waste of phosphorus resources and environmental pollution.On the other hand,the cost price of the diet is also raised by excessive addition of phosphorus.With the rapid development of the layers industry,the recommended phosphorus addition amount of the chicken feed standard in our country is not suitable for the development concept of China's green environmental protection animal husbandry.This test provides theoretical support for the accurate assessment of phosphorus requirements in laying hens from three perspectives:1)Using mono-dicalcium phosphate?MDCP?as phosphorus source,research the effects of different nPP levels on laying performance,bone development and serum indexes of laying hens fed with commercial diets?including 2000FTU/kg phytase?.2)The phytase was removed on the basis of the original diet formula,and further study the effect of nPP level on laying performance and phosphorus metabolism in laying hens.3)Using metabolomics technology to analyze the dynamic changes of serum small molecule metabolites in laying hens,to explore the changes of differential metabolites and metabolic pathways under three levels of nPP?low,normal,high?,and to study the mechanism of phosphorus homeostasis in laying hens.Experiment 1:Effects of non-phytate phosphorus levels on laying performance and bone quality in 25-40 week-old laying hens.This experiment used a single factor completely randomized trial design,with MDCP as the phosphorus source,the phosphorus addition levels were 0,0.05%,0.10%,0.15%,0.20%,0.25%,0.30%,a total of 7 treatment groups,selected 504 Healthy 25-week-old Hy-line brown-shell hens were randomly assigned to each group,with 6 replicates per treatment and 12 chickens per replicate.The trial lasted for 16 weeks and the pre-feeding period was 3 weeks.Every treatment group used corn-soybean meal-type diets with consistent calcium levels and 2000 FTU/kg phytase.The production performance was measured during the test period,and eggs,bones,serum,intestinal mucosa and feces were collected for egg quality,bone quality,serum biochemical indicators,intestinal transport vector gene expression and fecal phosphorus content.The result showed that the housed laying rate of 0.27%nPP group and 0.32%nPP group were significantly higher than that of0.37%nPP group and 0.42%nPP group?P=0.046?at the age of 37-40 weeks.There was no significant effect on egg production rate,daily egg production,average egg weight,average feed intake,feed-to-egg ratio and failure-egg rate?P>0.05?among different nPP levels in other periods.There was no significant change in egg quality?egg-shaped index,eggshell strength,eggshell thickness,yolk color,albumen height and Haugh unit?at 35th and 40th week with the change of nPP level?P>0.05?.No significant differences in serum calcium,phosphorus,alkalinephosphatase,calcitonin,parathyroidhormoneand1,25-dihydroxyvitamin D?1,25-?OH?₂D₃?levels among different groups?P>0.05?.Bone calcium,phosphorus,ash content and tibia strength were not affected by different nPP levels?P>0.05?.The expression of NaPi-IIb gene in the duodenum of 0.17%nPP level group was significantly higher than that of other treatment groups?P<0.001?.There was no significant difference in the expression level of NaPi-IIb gene between the treatment groups?P>0.05?.The expression of duodenal CaBP-d28k gene in the 0.17%nPP level group was significantly higher than that in the 0.27%,0.37%,and 0.42%nPP levels?P=0.032?.The CaBP-d28k expression of the 0.32%nPP level in the jejunum was significantly higher than that of other treatment groups?P=0.014?.With the continuous improvement of nPP level,the phosphorus excretion of laying hens also increased,showing an upward trend?P<0.05?.The results of this experiment indicated that 0.12%nPP,3.8%calcium and 2415 IU of vitamin D3 in the basal diet containing 2000 FTU/kg phytase were able to meet the margin of the nPP requirement of layers?25-40 week?.Moreover,this might be a potential way to reduce feed cost and diminish environmental concerns without compromising the egg production of laying hens.Experiment 2:Effects of non-phytate phosphorus levels on laying performance and bone quality in 41-55 week-old laying hens.Based on the first experimental formula,we no longer added phytase to the diet,and further explored the effects of nPP levels on laying performance and bone development in laying hens.This experiment used a single factor completely randomized trial design,with MDCP as the phosphorus source,the phosphorus addition levels were 0,0.05%,0.10%,0.15%,0.20%,0.25%,0.30%,a total of 7 treatment groups,selected 378 Healthy41-week-old Hy-line brown-shell hens were randomly assigned to each group,with 6replicates per treatment and 9 chickens per replicate.The trial lasted for 15 weeks.Every treatment group used corn-soybean meal-type diets with consistent calcium levels and no phytase.Test method is the same as experiment 1.The results showed that the housed laying rate of basic group,0.27%nPP group and 0.32%nPP group were significantly higher than that of 0.42%nPP group?P=0.020?at the age of 41-44 weeks.There was no significant effect on egg production rate,daily egg production,average egg weight,average feed intake,feed-to-egg ratio and failure-egg rate?P>0.05?among different nPP levels in other periods.Egg-shaped index,eggshell strength,eggshell thickness,egg yolk color,protein height,and Haugh units did not significantly be affect by different nPP levels?P>0.05?.The serum phosphorus content of the basal diet group and the 0.17%nPP level group was significantly higher than that of the 0.22%nPP level group,the 0.32%nPP level group,and the 0.37%nPP level group?P=0.009?.There is no significant effects on blood calcium,alkaline phosphatase,calcitonin,parathyroid hormone and 1,25-?OH?2D3 in laying hens fed with different nPP levels?P>0.05?.The tibia calcium,phosphorus,ash content and breaking strength were not significantly affected by the change in nPP gradient?P>0.05?.There was no significant differences in duodenal NaPi-IIb gene expression among the treatment groups?P>0.05?.0.32%and 0.42%nPP levels can significantly increase the expression of NaPi-IIb gene in jejunum?P=0.008?.The expression of CaBP-d28k gene in duodenum and jejunum can be significantly promoted by 0.42%nPP level?P=0.016,P=0.001?.With the increasing level of nPP level,the phosphorus excretion of laying hens tends to be excreted,showing an increasing trend?P>0.05?.This experiment shows that laying performance,egg quality and bone development in laying hens are not adversely affected with 0.12%nPP,3.8%Ca and2415 IU of vitamin D₃ when no additional phytase is added to the corn-soybean meal diet;In general,when the average feed intake is 130 g,the 0.12%nPP level?153.12 mg?in the corn-soybean meal diet can meet the margin of the nPP requirement of maintenance and production of layers in laying period?41-55 weeks old?.The addition of inorganic phosphorus can be appropriately reduced.Experiment 3:Screening and correlation analysis of serum sensitive differential metabolites in laying hens.Based on the serum samples collected in Experiment 2,we chose three treatment groups with a phosphorus addition level of 0,0.15,and 0.25%for non-targeted metabolomics analysis,and performed path enrichment analysis and selection on the obtained differential metabolites to determine the gene expression of the key enzymes.The results showed that a total of 29 sensitive differential metabolites were detected including 10 kinds of amino acids,6 kinds of organic acids,4 kinds of fatty acids,3 kinds of saccharides,1 amine,1 polyol,1nucleic acid and 4 other substances after comparison with control group,0.15%MDCP and0.25%MDCP.We found that as the level of nPP increased,all amino acids and fatty acids increased,the content of organic acids and sugars related to energy metabolism was decreasing?P<0.05?.The gene expression of the SUCLG1 subunit of the succinic acid CoA synthetase in the basic group was significantly higher than that in the 0.25%MDCP group?P<0.05?,phenylalanine hydroxylase,tyrosine transaminase,and 2-ketoglutarate dehydrogenase were not significantly affected by the changes in MDCP?P>0.05?after determination of the biosynthesis of phenylalanine,tyrosine and tryptophan and the TCA cycle.The results indicated that,in the low-phosphorus state,fatty acids such as arachidonic acid and arachidic acid tended to catabolize into the tricarboxylic acid cycle to produce energy,blood sugar concentration,the content of citric acid,and?-ketoglutaric acid were increased,and the tricarboxylic acid cycle were accelerated;under high phosphorus conditions,the free amino acid content in the blood of the laying hens was increased,pathways such as phenylalanine metabolism were activated,the deamination were enhanced,and the nitrogen excretion was increased.The decrease in blood glucose and intermediate content results in a decrease in the efficiency of the tricarboxylic acid cycle.In conclusion,the 0.12%nPP level had no adverse impact on laying performance and bone quality in laying hens fed with a corn-soybean meal-based diet containing 3.8%Ca,2415 IU vitamin D₃,and 2000 FTU/kg phytase?added from 25-40 week?.Poultry diets allow to be formulated with less amount of inorganic phosphate supplementation because the application of phytase.Under low phosphorus level,layers may promote energy metabolism pathways such as glycolysis,aerobic oxidation of sugars,and TCA cycles,reduce the efficiency of energy-consuming pathways such as amino acid metabolism and fatty acid metabolism to regulate the body's phosphorus homeostasis.In the future,high-dose phytase can be used in combination with low-inorganic phosphorus to reduce feed costs and deminish phosphorus excretion in order to comply with the development concept of economic and environmentally-friendly ecological animal husbandry.