Ultrastructural characteristics of ostrich eggshell: outer shell membrane and the calcified layers

The ultrastructure of the eggshell of the domestic hen has been well resear ched and structural studies of other avian species, such as the ostrich, of ten base their interpretation of egg shell structure on that of the chicken . In the ostrich, lowered hatchability and hatching trauma may be due to sh ell ultrastructural abnormalities. In the present study the ultrastructure of the calcified portion, and the outer shell membrane (OSM), of domesticat ed ostrich eggshells was investigated using standard electron microscopic t echniques. Transmission and scanning electron microscopy studies demonstrat ed intimate contact between cup-shaped structures present on the OSM and th e mammillary layer of the calcified portion of the shell. The initial calci um carbonate growth of the calcified shell was of a dendritic nature with n ucleation sites on the surface of the cup's contents. The dendritic growth gave way to a more randomly-orientated, smaller crystallite growth structur e, which changed in form as it neared the vertical crystal layer (VCL). The VCL is described as being both a morphous and 'crumbly' depending on the p lane of fracture. These observations suggest that firstly, initial calcific ation is contained within the cups and is then directed outwards to form th e shell and that secondly, the VCL may contain an evolutionary, calcified c uticular layer. These observations serve as a baseline for studies investig ating the effect of shell structure and strength on hatchling trauma and th e influence of maternal diet.