Environmental and Physiological Factors Influencing the Formation of the Eggshell of the Domestic Fowl

Fraser, Alexander Charles (1996) Environmental and Physiological Factors Influencing the Formation of the Eggshell of the Domestic Fowl. PhD thesis, University of Glasgow.

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The thesis begins with a comparison of four egg production systems currently in commercial use within the UK, namely battery, perchery, modified free range and traditional free range. The comparison involved traditional, material and ultrastructural measures and was carried out in order to assess the effect of the various production environments on shell structure and quality. No definitive order of rank was obtained, however, the results obtained indicate that each system has the potential to provide well structured eggshells throughout lay, providing that management of a high standard is maintained. The degree of environmental control offered by the battery system is reflected in terms of stable shell quality performance, while a poorer performance from the perchery is attributed to social order dysfunction. It is, however, acknowledged that many of the behavioural needs of the birds, such as the ability to nest, scratch and perch, are not met in the battery environment. An investigation into battery cage enhancement by means of perch provision and increased space allowance per bird was therefore carried out. Provision of a perch, when all birds had access to that perch, resulted in improved shell ultrastructural quality. If not all birds had access to the perch social stability was disrupted and ultrastructural quality compromised. In addition, force molting was also shown to have a beneficial effect on eggshell quality. This however could not be explained purely in terms of the shells inorganic component. These investigations were combined with a comprehensive review of the welfare requirements of the laying hen and how they are variously met and compromised within each system. The use of ultrastructural shell quality assessment was shown to provide an insight into the birds homeostatic mechanisms on a daily basis. It has therefore been suggested that it be added to the range of criteria currently used to evaluate the overall welfare status of the laying hen. As not all of the observations regarding shell quality performance could be explained in terms of the inorganic fraction of the shell alone, the role of the shell's organic matrix was highlighted. In particular, constituent proteins such as keratan sulphate, dermatan sulphate and ovocleiden-17 (OC-17) were investigated. Differences between etched (without membranes) and nonetched (with membranes) shells of good and poor quality were also investigated. Ultrastructural examination of eggshell matrix revealed a complex architecture that differs within each of the major zones within the shell. Its appearance in areas of the shell associated with crystal nucleation (mammillary cores), rapid growth (palisade layer) and termination (vertical crystal layer and cuticle) indicated a relationship between structure and function. As a result of this investigation a hypothesis has been developed regarding possible roles for the vesicles associated with the organic matrix of the shell. Extra and intramineral matrix proteins from good and poor quality, etched and nonetched shells were solubilised by sequential extractions using guanidine HCI and EDTA prior to SDS-PAGE. The matrix subunit protein OC-17 was demonstrated in all but the poor quality nonetched extramineral fraction and no differences in profiles were found between etched and nonetched shells. There is evidence to suggest that removal of the eggshell membranes by plasma etching gives a more accurate picture of the composition of the extramineral fraction of the organic matrix than previously obtained. Addition of soluble extra and intramineral proteins to a metastable solution of calcium carbonate was shown to modify the morphology of calcite crystals formed in vitro. This suggested that both these constituents of eggshell matrix are involved in the regulation of calcite crystal growth during the formation of the eggshell, contrary to the findings of previous researchers who have demonstrated an effect solely with the intramineral fraction. Immunohistological studies demonstrated the presence of OC-17 in the shell membranes, the mammillae, the palisade and vertical crystal layers. The presence of OC-17 in the vertical crystal layer indicated that this region contains an organic matrix component. Little difference in the distribution of OC-17 was demonstrated between good and poor quality shells. These results provide a foundation for future research on the organic fraction of the eggshell and have reinforced the fact that such studies are in their infancy. They also highlight the fact that this material has, by and large, been ignored in terms of shell quality assessment to date. It was concluded that a better understanding of the mechanisms involved in the biogenesis of the calcified egg shell would benefit the poultry industry at every level and would also pave the way for improvements in many other disciplines.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: M M Bain
Keywords: Veterinary science, Animal sciences, Physiology
Date of Award: 1996
Depositing User: Enlighten Team
Unique ID: glathesis:1996-75594
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 19:21
Last Modified: 19 Nov 2019 19:21
URI: http://theses.gla.ac.uk/id/eprint/75594

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