Ultrastructure of The Mammillary Region of Low Puncture Strength Avian Eggshells

177

105

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.

Section: Importance Of Shell Ultrastructurementioning

confidence: 95%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of the microstructure on the shell strength of eggs laid by hens of different ages

Rodríguez‐Navarro¹,

Kälin²,

Nys³

et al. 2002

177

105

“…Perhaps the eggshell could be considered as the end product of a genetically-controlled manufacturing process, which is subject to modification depending upon an individual bird's harmony with its environment. For example, the greatest variation in the ultrastructural organisation of the eggshell has been shown to take place in the mammillary layer (Bunk and Balloun, 1978;Watt, 1985;Solomon, 1985Solomon, , 1990, which is characterised by the presence of many naturally occurring fissures where adjacent mammillae fuse. Such 'intermammillary spaces' could be regarded as defects as they vary both in depth, size and distribution (Van Toledo et al, 1982).…”

Section: Introductionmentioning

confidence: 97%

Eggshell strength: A relationship between the mechanism of failure and the ultrastructural organisation of the mammillary layer

Bain

1992

1. Stress analysis using modern computer modelling techniques indicated that the shell should fail in tension as a result of the accumulation of stress at its inner most surface with the characteristic notched appearance of the mammillary layer providing the ideal crack initiation site. 2. Practical observations however indicated that crack initiation does not inevitably lead to catastrophic failure. This partly explains why previous attempts to predict shell failure from classical engineering theory underestimated the actual force required to break an egg. 3. Crack initiation should now be denned as localised trauma, characterised by a series of radial cracks which propagate outwards from the load point at first in a stable manner. As the interaction between the shell and its loading environment continues, one or more of these minor cracks become unstable, thus giving rise to catastrophic failure. 4. The fracture toughness of the eggshell is a measure of its resistance to unstable crack growth and in this respect there appears to be a link between the latter and the structural organisation of the mammillary layer.

“…Thus the diversity of cuticular coverage was explored by Board and Sparks between 1973 and 1991 and confirmed as an infrequent accessory rather than an inherent aspect of the true shell by Watt (1989) and Nascimento (1992). Simons in his thesis entitled "Ultrastructure of the hen's eggshell and its physiological interpretation" (1971), truly opened the door on the complexities of shell formation and so stimulated the interest of those to follow such as Robinson and King (1970) and Bunk andBalloun (1977, 1978) who illustrated the nature of the bonding between the membrane fibres and the 6 S. E. SOLOMON shell and found a correlation between ultrastructure and mechanical weakness. Likewise Van Toledo et al (1982) explored the relationship between shell structure and function.…”

Section: Eggshell Structurementioning

confidence: 97%

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

Solomon¹

1999

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.