Dietary Manganese Supplementation Modulated Eggshell Quality In Laying Hens

Eggshell quality is one of the most important economic and apparent characteristics of poultry eggs,and nutritional modulation of eggshell quality is an efficient way to solve eggshell problems.This dissertation mainly studied the mechanism of dietary Mn supplementation modulated eggshell quality in laying hens by using inorganic and organic sources,which was mainly focused on shell ultrastructure and its dynamic changes of shell formation.Experiment 1:Effect of dietary supplementation of organic or inorganic manganese on eggshell quality,ultrastructure and components in laying hens.A total of 1,080 46-wk-old Jing Brown hens were fed a basal diet?Mn,32.7 mg/kg?for 2 wks and then randomly allocated to 9 groups that were fed a basal diet?control?or the basal diet supplemented with inorganic?MnSO₄·H₂O?or organic?amino-acid-Mn,8.78%?Mn at 40,80,120,or 160 mg per kg of feed for 8 wks.Each group had 8replicates of 15 hens.The results showed that dietary Mn supplementation did not affect the performance of hens?P>0.05?.Dietary Mn supplementation resulted in linear and quadratic increases of breaking strength and thickness in both inorganic and organic forms?P<0.05?,but fracture toughness increased quadratically only in organic groups?P<0.05?.Linear and quadratic effects on effective thickness and mammillary thickness were observed with Mn supplementation from inorganic and organic sources?P<0.05?,and lower mammillary thickness was observed in organic groups?P<0.05?.However,the width of mammillary knobs decreased quadratically only with the supplementation of organic Mn?P<0.05?.Dietary Mn supplementation had a quadratic effect on the shell Mn content in both inorganic and organic forms?P<0.05?.Linear and quadratic effects on the content of sulfated glycosaminoglycans?GAGs?were observed only in calcified eggshell with inorganic Mn supplementation?P<0.05?,while the supplementation of organic Mn had a quadratic effect on sulfated GAGs content in both calcified eggshell and membranes?P<0.05?.Overall,dietary Mn supplementation,regardless of the source,could increase breaking strength and thickness by improving the ultrastructure,which partly results from increased sulfated GAGs content in the eggshell.Moreover,the supplementation of organic Mn could increase fracture toughness by decreasing the width of mammillary knobs,which is partially due to increased sulfated GAGs content in the membranes.According to the eggshell breaking strength and thickness,a supplement of 110¹20 mg Mn per kg feed from monohydrate Mn sulfate or 80⁹0 mg Mn per kg feed from amino acid-Mn complex was optimal of their sources respectively.Experiment 2:Dietary manganese supplementation modulated mechanical and ultrastructural changes during eggshell formation in laying hens.It was done by using the optimal levels of organic and inorganic Mn.A total of 270 62-wk-old Hy-Line Brown hens were fed a basal diet containing 25.1mg Mn per kg feed for 2 wks,after which they were randomly allocated into 3 groups and fed a basal diet?control?or the basal diet supplemented with 120 mg Mn per kg feed from monohydrate Mn sulfate?an inorganic source of Mn?,or 80 mg Mn per kg feed from an amino acid-Mn complex?an organic source of Mn?for 12 wks.For each group,6 replicates of 15 hens were used with 1 hen per cage.Dietary Mn supplementation significantly increased eggshell-breaking strength and thickness in laying hens?P<0.05?.In neither was the elasticity of their eggshell membranes,measured during the nucleation and the initial deposition stages,affected by dietary Mn compared with the control?P>0.05?,whereas the breaking strength of the eggshells was greater at the linear and terminate deposition stages compared with the control?P<0.05?.Dietary Mn supplementation decreased the width of the mammillary knobs and the proportion of mammillary thickness,and increased the proportion of effective thickness of the whole eggshells?P<0.05?.Ultrastructural changes during the eggshell formation indicated that dietary Mn supplementation increased the nucleation-site and mammillary-knob densities,decreased the mammillary knob thickness,and increased the proportion of effective thickness and total thickness of the eggshells compared with the control?P<0.05?.Therefore,dietary Mn supplementation could improve the breaking strength and ultrastructure of the eggshells during their formation,and the mammillary and palisade layers were both the crucial structure affected by Mn.Experiment 3:The mechanism of dietary manganese supplementation affected mammillary knobs of shell ultrastructure in laying hens.A total of 225 54-wk-old Hy-Line Brown layers were fed a basal diet containing 27.5 mg Mn per kg feed for 2 wks,after which they were randomly allocated into 3groups and fed a basal diet?control?or a basal diet supplemented with 120 mg Mn per kg feed from monohydrate Mn sulfate?an inorganic source of Mn?,or 80 mg Mn per kg feed from an amino acid-Mn complex?an organic source of Mn?for 10 wks.For each group,5 replicates of 15 hens were used with 1hen per cage.Compared with the control,dietary Mn supplementation increased the mammillary-knob density of eggs at 9.5 h post-oviposition?P<0.05?.The Mn content in blood and eggshell gland were both improved by dietary Mn supplementation in inorganic and organic forms?P<0.05?,but the blood Mn content was higher in inorganic Mn treatment compared with that in organic treatment?P<0.05?.The results from RNA sequencing and quantitative real-time PCR analysis of the eggshell gland showed that dietary Mn supplementation affected the protein glycosylation and glycan metabolism and improved the expression of proteoglycans and glycoproteins in the eggshell gland?P<0.05?.Therefore,dietary Mn supplementation could affect the protein glycosylation and glycan metabolism and improve the expression of proteoglycans and glycoproteins in the eggshell gland,and thus improved the mammillary knob density of eggshell ultrastructure.Overall,dietary Mn supplementation can modulate protein glycosylation and glycan metabolism,and improve the expression of proteoglycans and glycoproteins in the eggshell gland,regulate the mammillary knobs formation and improve the shell ultrastructure,and thus improve eggshell quality.