1. The eggshell is a bioceramic material constructed of columnar calcite crystals preferentially oriented with their c-axis perpendicular to the shell surface. 2. The influence of microstructure (crystal size, shape and crystallographic orientation of crystal grains) on the mechanical properties of eggshells (shell strength) was investigated using eggs from hens of different ages. 3. There was a strong correlation between crystallographic texture and the strength of the eggshell in the case of eggs laid by young hens. The strength of eggshells increased as the preferential orientation of the crystals constituting the eggshell decreased. 4. By comparing two age populations, the effect of hen age on eggshell properties was evaluated. In general, eggshells from aged hens had a lower breaking strength (less than half that of those laid by young hens) and showed a greater variability in their structural properties such as thickness, grain morphology and crystallographic texture. 5. Texture analysis revealed that shells from eggs laid by aged hens have two preferred crystal orientations, after (001) and (104), compared with mainly one, after (001), in eggs laid by young hens. 6. These observed changes in eggshell properties could be due to changes in the organic matrix of the eggshell associated with ageing of the hens.

The biomineral phase of avian eggshell is characterized at the nanostructure scale and correlated with functional properties.

(1) Background: Nowadays the industry aims to improve lay persistency for extended cycles (100 weeks or longer) to make egg production more sustainable. However, intensive egg production challenges hen health, inducing severe osteoporosis and the incidence of bone fractures. In this study, the relationship between bone quality and egg production, and/or eggshell quality, was evaluated at the end of an extended laying cycle of 100 weeks, comparing groups of hens with different production and eggshell quality parameters; (2) Methods: Quality parameters of egg (as weight, egg white height), eggshell (as thickness, weight, breaking strength, elasticity and microstructure) and tibiae bone (weight, diameter, cortical thickness, ash weight, breaking strength, medullary bone) were determined; (3) Results: Hens from groups with a high egg production and good eggshell quality have poorer bone quality (lower ash weight and lesser amount of medullary bone). However, Pearson’s correlation analysis shows no clear relationship between bone and egg/eggshell parameters. (4) Conclusions: Bone and egg production/eggshell quality are independent and can be improved separately. Medullary bone has an important contribution to bone mechanical properties, being important to accumulate enough bone medullary bone early in life to maintain skeletal integrity and eggshell quality in old hens.

For a fuller understanding of the functionality of the eggshell cuticle, we conducted a detailed study using a wide array of analytical techniques (s