The Research Of Eggshell Chemical Components And Ultrastructure In The Late Phase Of Production Of Laying Hens

Eggshell quality is an important economic index in laying hens’ production.Eggshell quality is one of the key problems that affect the economic benefits.This study took Hy-Line Brown laying hens as research object.Firstly,we observed eggshell quality changes from the peak to the late phase of production,the key period of eggshell quality decline in the late phase of production was identified,and the possible reasons for the decline of eggshell mechanical properties were explored from the aspects of ultrastructure and chemical composition;the eggshell ultrastructure and chemical components with different strength and defects in the late phase of production were further explored.The purpose of this study was to provide basic data and reference for the regulation of eggshell quality in the late phase of production.Experiment 1.The changes of eggshell quality of Hy-Line Brown layers from the peak to the late phase of production.We observed the changes of eggshell physical and mechanical properties,the key period and reasons of eggshell quality decline in the late phase of production were identified.The result showed that: 1)Egg weight,egg length and eggshell area of 31 to 80-wk-old were increased linearly(P< 0.01).Eggshell weight,eggshell percentage,eggshell thickness and eggshell index were increased and then decreased with hen age(P < 0.05).After 50-wk-old,eggshell strength and eggshell fracture toughness were decreased significantly(P <0.05),and reached the lowest value from 65 to 80-wk-old(P< 0.05).According to properties of eggshell quality,the laying cycle was divided into 3 stages of 31 to50-wk-old,55 to 60-wk-old and 65 to 80-wk-old.For eggshell ultrastructure,mammillary thickness and rate of 70 and 80-wk-old were significantly lower than those of 31 to 60-wk-old(P < 0.05),and mammillary knob density was significantly lower than that of 31-wk-old(P < 0.05).Calcium content per unit area of 70 and 80-wk-old were decreased significantly(P < 0.05).Phosphorus content of 60,70 and80-wk-old was significantly lower than others(P < 0.05),while the phosphorus content per eggshell and per unit area were significantly lower than those of 31-wk-old(P < 0.05).This trail suggested that eggshell mechanical properties were decreased significantly after 65-wk-old,the changes of eggshell ultrastructure layer thickness and rate might contribute to the decrease of eggshell mechanical properties in the laying cycle.The decrease of eggshell phosphorus content might be one of the reasons for the decrease of eggshell mechanical properties from 60 to 80-wk-old.From 70 to 80-wk-old,eggshell ultrastructural variation and the decrease of eggshell calcium content per unit area might aggravate the decrease of eggshell mechanical properties.Experiment 2.The changes of eggshell ultrastructure and components of different strength eggshell in the late phase of production.Eggs were collected from 680 healthy 73-wk-old Hy-Line Brown laying hens.The high and low strength groups were distinguished by the "mean ± 1.6 × SD" of eggshell strength,and the "mean ± 0.15 × SD" was regarded as the medium strength group.The result showed that eggshell thickness,weight,percentage,index,fracture toughness,calcified thickness,mammillary thickness,effective thickness and percentage were decreased with eggshell strength(P < 0.05),mammillary rate was lower in high strength group(P < 0.05).Calcium content per eggshell and per unit area of low strength group were lower than high strength(P < 0.05).Phosphorus content per eggshell and per unit area were higher in high strength group(P < 0.05).Eggshell organic matter and total protein content were higher in low strength group(P < 0.05).In summary,the eggshell deposition of mineral and calcium were decreased,and organic matter content was increased.Calcified layer thickness and effective layer thickness were decreased,which resulted in the decrease of eggshell thickness,weight and rate.These are the important differences of eggshell with different strength in late phase of production;In addition,high strength eggshell had higher phosphorus content.Experiment 3.The changes of eggshell ultrastructure and components of defected eggshell in the late phase of production.The chicken selected was same to experiment 2.The types of eggshell defects and incidence was counted for 4 consecutive days,and the highest frequency of little pimpled eggshell(16.24%)was selected as the research object.According to the severity of little pimple,the score was from 1 to 6,and 0 was normal eggshell.The result showed that eggshell strength of score 5 and 6(defected area ≥ 45%)were significantly lower than score 0(P < 0.05).Eggshell thickness,calcified layer thickness,eggshell weight and index were significantly decreased(P < 0.05).Calcium content of score 3to 6(defected area ≥ 20%)was significantly decreased,calcium content per eggshell and per unit area of score 5 and 6(defected area ≥ 45%)were significantly decreased(P < 0.05),and little pimples and cracks were increased.The experiment suggested that eggshell strength was decreased with the increase of the area of little pimples on eggshell surface;the area of little pimples on eggshell surface < 45%(score< 5)had no significant effect on eggshell mechanical properties,and the area of little pimples on eggshell surface ≥ 45%(score 5 and 6)was decreased significantly.The decrease of calcium deposition,eggshell thickness and calcified layer thickness may be the main reason for the decrease of mechanical properties.In conclusion,eggshell mechanical properties were decreased significantly after 65-wk-old of HyLine Brown layers.The changes of eggshell ultrastructure thickness,rate and mammillary layer may contribute to the decreased of eggshell quality in the laying cycle,and the rate of mammillary and effective layer was the structural trait in the late phase of production.The decrease of eggshell calcium,eggshell calcified layer thickness and effective layer thickness may result in the decrease of eggshell thickness,weight and rate,which was an important difference of different strength eggshell in the late phase of production,and was also the main reason for the decrease of eggshell strength with little pimples.