Effect Of Dietary Manganese Sources And Supplemental Levels On Eggshell Quality Of Laying Hens

Eggshell quality is of primary concern to the egg industry as the commercial processing andmarketing of eggs usually causes a high rate of cracked or broken eggshells. It is generally accepted thateggshell quality decreases with hen age, and the incidence of cracked eggs can exceed20%at the end ofthe laying period. Many nutritional approaches to improving eggshell quality have been explored.Numerous studies have concentrated on the effects of macro minerals (calcium and phosphorus) andvitamin D3on eggshell and bone quality. It is well known that macro minerals act as an eggshellstructural component and play an essential role in eggshell function. However, the relationship betweentrace elements and eggshell quality still awaits further study.Manganese (Mn) is an important traceelement in poultry nutrition, this study explored the mechanism of effect of Mn supplementation oneggshell quality, and investigated the bio-efficacy of organic Mn compare to the inorganic Mn oneggshell quality.Experiment1.Effect of dietary Mn supplementation on eggshell qualityThis study investigated the effect of dietary manganese (Mn) supplementation on eggshell quality,ultrastructure, glycosaminoglycan (GAG) and uronic acid content, and mRNA and protein expression ofGalβ1,3-glucuronosyltransferase (GlcAT-I). A total of216layers (Hy-Line Grey) at age50wk weredivided into three groups. In the first8wk of the12wk feeding trial, all groups were fed a basal dietthat met all layer nutrient requirements except for Mn. In the last4wk, each group was fed one of threediets supplemented with Mn levels at0,25, or100mg Mn/kg. Dietary Mn deficiency did not affect theegg performance of layers. Dietary Mn supplementation significantly improved the breaking strength,thickness and fracture toughness of eggshells (p<0.05). In photographs of eggshell ultrastructure, thesize of mammillary cones and cracks in the outer surface were decreased by dietary Mnsupplementation. The contents of glycosaminoglycans (GAGs) and uronic acids in eggshell membranewere significantly increased by dietary Mn addition (p<0.05). This result was further confirmed byincreased mRNA expression and protein expression of GlcAT-I when Mn was added to the diet. Thisstudy suggests that dietary Mn supplementation can improve eggshell quality by enhancing the GAGand uronic acid synthesis in the eggshell glands, which can affect the ultrastructure of eggshells.Experiment2. Effect of dietary Mn supplementation on matrix protein in the eggshellThis study investigated the effect of dietary Mn supplementation on matrix protein expression inthe eggshell. The eggshell fragments were randomly sampled from the replicates of0mg/kg or100mg/kg Mn supplementation treatment. Isotope tags for relative and absolute quantitation technologywas applied to investigate the difference of matrix protein expression in the eggshell. Dietary Mnsupplementation significantly influence the68matrix proteins expression in the eggshell. There were31 matrix proteins up regulated and38matrix proteins down regulated by the dietary100mg/kg Mnsupplementation. These up or down regulated matrix proteins were related to eggshell calcification orlayer’s immunity. In conclusion, dietary Mn supplementation influenced the process of eggshellcalcification and layer’s physiological status.Experiment3.Effect of different sources and levels dietary of Mn supplementation on eggshellquality and bio-efficacy comparison of organic and inorganic Mn on eggshell quality of layinghens.This study investigated the effect of different Mn resources supplementation on eggshell qualityand compared the bio-efficacy of organic Mn to the inorganic Mn on eggshell quality. A total of648layers (Hy-Line brown) at age50wk were divided into nine groups. In the first4wk of the12wkfeeding trial, all groups were fed a basal diet that met all layer nutrient requirements except for Mn. Inthe left8wk, each group was fed one of nine diets supplemented with different Mn resources at:0mg,inorganic25,50,100,200mg; organic (Amino acid manganese, AA-Mn)25,50,100,200mg Mn/kg.Dietary Mn deficiency did not affect the egg performance of layers (p>0.05). Dietary Mnsupplementation significantly improved the breaking strength, thickness and fracture toughness ofeggshells at62wk (p<0.05). Dietary supplementation of AA-Mn100mg/kg or200mg/kg Mnsignificantly reduced the egg weight (p<0.05), but there were no difference between the inorganic Mntreatments(P>0.05). Compare to the control group, dietary supplementation of100mg or200mginorganic or organic Mn/kg significantly increased the breaking strength, thickness and fracturetoughness of eggshell at the age of60wk or62wk. On the equimolar basis, there were no difference ofeffect between AA-Mn and inorganic Mn treatments. Regression analysis revealed the AA-Mn was159.1%(breaking strength),107.8%(elastic modulus) and198.2%(thickness) as efficacious asinorganic Mn on the quimolar basis.Experiment4.Modeling of mechanics of eggshell ultra-structureThis study discussed the mechanics of eggshell ultra-structure affected by dietary Mnsupplementation. A model of eggshell ultra-structure mechanic was set on the base of photographs ofscanning electronic microscope in experiment1. Formulas of material mechanics were applied to justifythe difference of ultra-structure lead to different stress in the eggshell. The eggshells with more compactand uniform mammilaries and thicker palisade layer were tested as with more compressive strength. Theconclusion justified from the eggshell model were in agreement with results from experiment1. Thisstudy revealed that dietary Mn supplementation can influence the mechanics of eggshell ultra-structure.