| As an important nutrient in poultry diet,phosphorus is one of the most important mineral elements in the body of the laying hens,which occupies the dominant position in the laying hens,especially in the egg production period.In the current livestock breeding process,the feeding standard of the laying hens is too old,and there is a high level of phosphorus added in commercial diet,resulting in a large amount of waste of phosphorus and excreta phosphorus.Meanwhile,the shadow price of phosphorus in the diet is higher and higher,the cost of breeding is increasing,and the demand for environmental protection of animal husbandry is also higher and higher in our country.Therefore,it is imperative to re-evaluate the nutrient requirements of phosphorus for laying hens,utilize the phosphorus source reasonably,reduce the excretion of fecal phosphorus,and realize green and environment-friendly breeding.This study is made up of three main parts : First,the addition of inorganic phosphorus were investigated on the basis of commercial practice diet(phytase content is 2,000 FTU/kg).Then,through the analysis of the nutrition process of laying hens under different phosphorus levels(without phytase),the nutritional requirements of laying hens for non-phytate phosphorus were evaluated,and the molecular mechanism of the effect of phosphorus level on laying hens was explored.The results of this study can provide a reference for the rational application of calcium phosphate feed additive in laying hens and healthy and environmentally friendly breeding.Experiment 1 Effects of different phosphorus addition levels on performance,egg quality,tibia characteristics,serum biochemical indexes and excreta phosphorus in laying hensThis experiment was conducted to investigate the effects of different phosphorus addition levels on performance,egg quality,tibia characteristics and serum biochemical indexes in laying hens,aiming to accurately evaluate the optimal nutrition requirement of nonphytate phosphorus for laying hens on the basis of commercial diet,and further providing a reference for reasonable application of phosphate feed additive and healthy environmental breeding on laying hens.A total of 504 healthy Hy-Line brown layers(26 weeks of age)with similar body weight were randomly divided into 7 groups with 6 replicates per group and 12 hens per replicate.According to the assigned treatment group,layers were fed with commercial-type diet supplementing 0,0.05%,0.10%,0.15%,0.20%,0.25% and 0.30% nonphytate phosphorus from DCP,respectively.Other nutrient levels were kept the same in diets.All diets contained 2000 FTU/kg phytase.Birds were allowed to adapt to experimental diets in the layer house for 3 weeks,the entire experiment period lasted for 12 weeks.Growth and egg performance were recorded during the trial.Eggs,serum and tibia were collected for detection of egg quality,biochemical paramaters and tibia quality after the trial.During the experiment,with the increasing of nonphytate phosphorus addition levels,different phosphorus addition levels didn't affect laying rate,average Egg weight,average daily feed intake,egg mass,feed-egg ratio and unqualified egg rate of laying hens(P>0.05).When compared with the control group,there was no significant difference in eggshell thickness,eggshell strength,albumen height,yolk color and haugh units among groups(P>0.05).What's more,different phosphorus addition levels have no effect on tibia breaking strength,ash,Ca and P contents,and same phenomenon was observed in serum Ca,P and ALP(P>0.05).In the current study,in the case of dietary containing phytase(2 000 FTU/Kg),the basal diet has meet phosphorus nutrient requirement for layers without the need of extra phosphorus addition.Therefore,maybe phytase can be used to satisfy production demand of layers and replace inorganic phosphorus addition completely in the diet,which can save phosphorus source and reduce phosphorus excretion,and further achieve the purpose of protecting environmental and sustainable development of resources.Experiment 2 Effects of dietary phosphorus levels on nutrition process in laying hensOn the basis of experiment 1,the phytase was removed from the diet.This experiment was conducted to analyze the effects of dietary non-phytate phosphorus levels on nutrition process in laying hens,aiming to evaluate the nutrition requirement of non-phytate phosphorus for laying hens and study on the molecular mechanism of the effect of phosphorus level on laying Hens,and further providing a reference for reasonable application of phosphate feed additive and healthy environmental breeding on laying hens.A total of 216 healthy Hy-Line brown layers(42 weeks of age)with similar body weight were randomly divided into 3 groups with 6 replicates per group and 12 hens per replicate.According to the assigned treatment group,layers were fed the same corn-soybean basal meals(without phytase)but containing 0.12%,0.27% and 0.37% nonphytate phosphorus,respectively.Other nutrient levels were kept the same in diets.Birds were allowed to adapt to experimental diets in the layer house for 3 weeks,the entire experiment period lasted for 12 weeks.Growth and egg performance were recorded during the trial.Eggs,serum,tibia,intestinal mucosa and uterus tissues were collected for egg quality,serum index,tibia quality and related gene detection of intestinal and uterine part.In this study,with the increasing of nonphytate phosphorus levels,different non-phytate phosphorus levels didn't affect laying rate,average Egg weight,average daily feed intake,egg mass,feed-egg ratio and unqualified egg rate of laying hens(P > 0.05).When compared with the control group,there was no significant difference in eggshell thickness,eggshell strength and yolk color among groups(P>0.05).What's more,different non-phytate phosphorus levels have no effect on tibia breaking strength,ash,Ca and P contents,and same phenomenon was observed in serum P and ALP(P>0.05).Compared with the control group,the 0.37 NPP group significantly increased the serum calcium level(P < 0.05).In the control group,the expression of Na P-IIb m RNA in duodenum was significantly increased(P < 0.05),and there is also a tendency to increase in the jejunum.The m RNA expression of Ca BP was similar to that of NAp2 b in duodenum and jejunum.The m RNA expression of OC116 increased significantly in basal diet group,and the excretion of fecal phosphorus increased with the increase of non-phytate phosphorus level.The results showed that 29 different metabolites were screened between Control group and0.25% DCP group,23 of them were up-regulated and 6 were down-regulated.Differential metabolites are mainly related to glucose metabolism,amino acids and fatty acids.The enriched metabolic pathways mainly revolve around the tricarboxylic acid cycle,amino acid metabolism,fat metabolism and so on,among which the most affected pathway is the phenylalanine biosynthesis pathway.The low phosphorus diet promoted the tricarboxylic acid cycle and enhanced the oxidative energy supply and the metabolism of amino acids and fat to some extent.In conclusion,the conventional commercial diet(0.12%NPP)or 154 mg/d non-phytate phosphorus intake has been able to meet the needs of laying hens for phosphorus nutrition.Under the low phosphorus level,laying hens can enhance the phosphorus retention rate through self-feedback regulation,and then maintain the phosphorus homeostasis.Phenylalanine may be a sensitive marker of response to dietary phosphorus level,and the dietary phosphorus level of laying hens may be evaluated by the content of phenylalanine in serum in production.In summary,in the case of dietary containing phytase(2 000 FTU/Kg),the basal diet has met phosphorus nutrient requirement for layers without the need of extra phosphate addition;A conventional commercial diet(0.12%NPP)or 154 mg/d non-phytate phosphorus intake has met the needs of phosphorus for laying hens at 41-55 weeks,so the amount of inorganic phosphorus can be reduced appropriately in the diet,even without supplementing inorganic phosphorus at all;Under the low phosphorus level,laying hens can enhance the phosphorus retention rate through self-feedback regulation,and then maintain the phosphorus homeostasis;Phenylalanine may be a sensitive marker of response to dietary phosphorus level,and the dietary phosphorus level of laying hens may be evaluated by the content of phenylalanine in serum in production. |
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