An egg ist ein ei, es un huevo, est un oeuf

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Abstract
1. Many of the mechanical tests devised to measure shell quality are inadequate because they fail to recognise the complex interaction between the organic and inorganic aspects of the eggshell. 2. Twelve structural modifications have been observed at the level of the mammillary layer and their presence correlated with a variety of environmental stress events. Occurring as they do in the basal layers of the shell, these morphological variants influence its mechanical properties. 3. The organic matrix proteins which complex with the calcium carbonate derive from a variety of sites within the oviduct and vary in their location within the fully formed shell. In vitro mineralisation reveals the significance of these proteins in the crystal growth mechanism. 4. The isolation and identification of the protein moiety in well-structured eggshells is an essential prerequisite to understanding the abnormalities in crystal growth observed in the shells of older birds challenged by disease and other undesirable 'on farm' events. 5. The eggshell is the daily indicator of the bird's harmony with its environment and as such provides a readily accessible and non invasive measure of welfare. The integration of these data with those derived from behavioural and biochemical testing should provide industry with a reliable numerical welfare index.