Evidence is presented to indicate that: a) The cuticular layer of the shell is rarely present as an even covering at any stage in the laying year. So, its role as a first line of defence is questionable. b) The shell membranes do inhibit bacterial transfer to some degree, even when they are structurally disrupted; however, if the challenge is great enough, then their function as effective barriers is reduced. c) In the absence of the shell membranes, Salmonella enteritidis Phage type 4 does not move freely across the shell, but it is either facilitated or inhibited in its passage by structural variation in the true shell, particularly at the level of the mammillary layer. Statistical data support in most instances a significant and positive correlation between the presence of structural defects and bacterial transfer. d) In a three tier battery system, a tier effect exists with respect to ease of translocation of microoganisms, with eggs from the top tier being more susceptible, i.e. structurally inferior. e) The results confirm earlier work that shell quality declines with age, and extends this finding to show that this morphological deterioration is accompanied by a decreased resistance to bacterial movement. f) Patent gas exchange pores, whilst obvious portals for bacterial ingress, are in this respect of secondary importance to structural defects within the shell. Evidence is also provided to substantiate the assumption that birds, irrespective of strain, display diverse shell structural quality. One of the strains evaluated (strain B) was structurally better than the other (strain A), at the beginning and middle of lay, and was also more capable of withstanding bacterial challenge in all three laying periods tested. 4. The housing system can influence shell quality; thus Barn and Battery eggs were structurally superior to their Range counterparts, at the end of lay. 5. The tagging of Salmonella with immunogold markers proved to be a valuable technique, which allowed a more precise localisation of the bacteria within the shell's ultrastructure, as viewed by the Scanning Electron Microscope (S.E.M.). This method gave support to other findings in this work, confirming that bacterial transfer was specifically encouraged by late fusion and alignment of the mammillae and pitting occurrences, with the cone layer probably implicated in the process of penetration in vivo. (now derestricted)
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:555720 |
| Date | January 1992 |
| Creators | Nascimento, Vladimir Pinheiro do |
| Publisher | University of Glasgow |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://theses.gla.ac.uk/3893/ |
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