Abstract
BackgroundLower eggshell quality in the late laying period leads to economic loss. It is a major threat to the quality and safety of egg products. Age-related variations in ultrastructure were thought to induce this deterioration. Eggshell formation is a highly complex process under precise regulation of genes and biological pathways in uterus of laying hens. Herein, we evaluated the physical, mechanical and ultrastructure properties of eggshell and conducted RNA sequencing to learn the transcriptomic differences in uterus between laying hens in the peak (young hens) and late phase (aged hens) of production.ResultsThe declined breaking strength and fracture toughness of eggshell were observed in aged hen group compared to those in young hen group, accompanied with ultrastructure variations including the increased thickness of mammillary layer and the decreased incidence of early fusion. During the initial stage of eggshell formation, a total of 183 differentially expressed genes (DEGs; 125 upregulated and 58 downregulated) were identified in uterus of laying hens in the late phase in relative to those at peak production. The DEGs annotated to Gene Ontology terms related to antigen processing and presentation were downregulated in aged hens compared to young hens. The contents of proinflammatory cytokine IL-1β in uterus were higher in aged hens relative to those in young hens. Besides, the genes of some matrix proteins potentially involved in eggshell mineralization, such as ovalbumin, versican and glypican 3, were also differentially expressed between two groups.ConclusionsAltered gene expression of matrix proteins along with the compromised immune function in uterus of laying hens in the late phase of production may conduce to age-related impairments of eggshell ultrastructure and mechanical properties. The current study enhances our understanding of the age-related deteriorations in eggshell ultrastructure and provides potential targets for improvement of eggshell quality in the late laying period.
Highlights
Lower eggshell quality in the late laying period leads to economic loss
Age-related deterioration in eggshell ultrastructure There was a significant increase in the thickness of mammillary layer (72.87 ± 6.47 vs. 81.98 ± 9.12, young vs. aged hens, P = 0.037), but a significant decline (P < 0.05) in effective thickness (316.38 ± 6.20 vs. 300.26 ± 17.64, P = 0.029) of aged hens relative to those of young ones (Fig. 1)
A recent study evaluated shell quality of eggs sampled every 5 wks, from 30 to 81 wk. of hen age and the results showed that eggshell from the peak phase (30–53 wk. of age) and the late phase (58–81 wk. of age) of production could be distinguished in terms of egg physical and eggshell quality attributes [23]
Summary
Lower eggshell quality in the late laying period leads to economic loss. It is a major threat to the quality and safety of egg products. We evaluated the physical, mechanical and ultrastructure properties of eggshell and conducted RNA sequencing to learn the transcriptomic differences in uterus between laying hens in the peak (young hens) and late phase (aged hens) of production. Great economic loss caused by lower eggshell quality is a major concern for egg industry and this problem can be more serious in the late laying period [1,2,3]. Eggshell in the late phase of production possessed lower breaking strength, accompanied with a greater variability in structural properties such as thickness, grain morphology and crystal texture [7]. The percentages of abnormal structure such as type B mammillae and late fusion in eggshell from aged hens were higher than those from young hens [8], which was thought to contribute to the impairment of mechanical properties. Age-related abnormalities in ultrastructure could be one reasonable explanation for the compromised shell quality in the late laying period
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