Antimicrobial defences of the avian egg

The successful proliferation of future avian generations is dependent on the ability of eggs to remain uncontaminated during incubation. Antimicrobial constituents are incorporated into the egg during its formation within the reproductive system of the hen. Traditionally, avian albumen is considered as the only defensive component of the egg while other egg structures (shell and membranes) are considered simply as physical barriers. In this thesis, the antimicrobial proteins identified in mature avian species and the evidence suggesting their incorporation in eggs is presented. Albumen of both domestic and wild avian species is investigated for its protein content and antimicrobial properties in order to investigate the effects of phylogeny and environmental pressures on the antimicrobial defences of the egg. Cuticle and outer eggshell protein extracts from both domestic and wild avian species as well as lipophilic outer eggshell components of domestic avian species are investigated in order to demonstrate the role of the eggshell in the antimicrobial defence of the avian egg. The role of selected eggshell proteins in the antimicrobial defence of the avian egg is investigated and discussed. The results presented demonstrate that antimicrobial defence in the avian egg is a much more complex system than previously believed. Egg white as well as eggshell specific proteins appear to enhance the antimicrobial defences of the egg. In addition, species-specific antimicrobial defensive strategies appear to be present in the eggs of avian species in response to unique environmental pressures.