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Press Info item.
19/04/2006
Reinforcing the natural defences of the egg
The aim of the European EggDefence project (1) was to improve the natural defences of hen eggs. The project was coordinated by the INRA Research Centre in Tours, France (2), in partnership with several European and Canadian teams. Its aim was to lay the groundwork for the new European directive 1999/74 that will go into effect in 2012 with the intention of establishing minimum standards for the protection of laying hens by modifying production systems. The EggDefence programme made it possible to identify new tools for improving egg quality by reinforcing its natural defences, and to optimise sanitary control at the level of production.
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95% of the eggs produced today come from hens raised in conventional cages. With animal welfare an increasing priority, the European Community has planned the implementation of a new production system as of 2012. This new system, better adapted to the welfare of the animal, must nevertheless be optimised to ensure the hygienic quality of eggs and to avoid their microbial contamination. Researchers involved in the European EggDefence1 project defined three key objectives for their programme in order to analyse and reduce the risk of contamination: first, to analyse the structure of the egg and the production factors that determine its quality; second, to reinforce the egg's natural defence systems and to improve the sorting of eggs at risk, and; finally, to inform professionals and consumers about the optimal conditions for egg production and conservation.
New production system
The new egg laying system raises the problem of food safety. New European regulations propose replacing conventional cages with furnished cages, where laying hens will have more ground surface per animal, perches, a nest and a dust bath, or, alternatively an aviary and free range system. These systems are better adapted to the welfare of the animals but require greater sanitary vigilance since the egg can be contaminated by surrounding dust or come in contact with polluted elements. The main risk for the egg is contamination by Salmonella enteritidis, responsible for 60% of food poisonings caused by this bacterium when consuming raw eggs. The EggDefence project made it possible to specifically identify contamination pathways of the egg by Salmonella bacteria and to propose solutions for attaining irreproachable sanitary quality in this new production system.
Contamination through the eggshell
Research has shown that bacterial penetration can take place through cracks or fractures in the eggshell. Its strength and solidity are therefore essential. Researchers working on the EggDefence project succeeded in identifying the genes coding for proteins that influence the formation of the eggshell; the existence of polymorphism on these genes explains some of the variability of eggshell solidity, making it easier to select hens that lay stronger eggs. Another factor to be controlled: overly rapid cooling of the egg just after it has been laid since this is conducive to the possible survival of Salmonella bacteria on the eggshell. Finally, the multiplication of Salmonella bacteria in the egg increases with high storage temperatures and long conservation. These factors are therefore to be taken into consideration when eggs are packaged and stored.
© INRA / C. SLAGMULDER - PCD2499-IMG0058.PCD
Electrophoretic analysis of proteins involved in the formation of the eggshell.
Protective proteins
Egg white has a natural antibiotic activity thanks to two proteins in particular, ovotransferrin and lysozyme. They act, respectively, by depleting the environment of iron, essential to bacterial growth, and by destroying the walls of some bacteria. This antibiotic activity was already known but researchers were able to show that it is partially inheritable and that hens can therefore be selected on the basis of the antibacterial activity of the egg white. These two proteins only explain part of the antimicrobial potential. Other antibacterial agents present in the egg white are yet to be identified.
Freshness control systems
The EggDefence programme also made it possible to identify several instantaneous measuring techniques to evaluate whole egg quality. Infrared light can be used to assess freshness by measuring the proportion of white liquid and the evolution of the pH inside the egg. Spectral light can be used to detect the presence of blood spots in the egg without opening it. Finally, other tools such as low-resolution mass spectrometry can be used to evaluate the internal quality of the egg or possible microbial contamination. The next step will consist of adapting one of these systems to an industrial application, particularly at the level of automatic sorters that control egg quality before they are put on the market.
This project that brings together 12 partners from several European countries (Germany, Belgium, Spain, Great Britain, Sweden) and Canada made it possible to study several of the factors leading to the bacterial contamination of eggs and to evaluate possible systems to more effectively select laying hens and improve the control and sorting of eggs. EggDefence will be followed by a new European project at the end of 2006, Rescape, whose priorities will be the development of selection methods based on the antimicrobial activity of the egg and the decontamination of the whole egg.
Sources:
Nys, Y., Gautron, J., Garcia-Ruiz, J.M., Hincke, M.T. 2004. Avian eggshell mineralization: biochemical and functional characterization of matrix proteins. Comptes Rendus Palevol, 3:549-562.
Messens, W., Grijspeerdt, Herman L., 2004. Eggshell penetration by Salmonella. World Poultry Sci. J., 61, 71-86.
De Ketelaere B., Bamelis F., Kemps B., Decuypere E., de Baerdemaeker J., 2004. Non-destructive measurements of egg quality. World Poultry Sci. J, 60, 289-302.
1 The European "EGGDEFENCE" project, QLRT-2001-01606, on the natural defences of the egg, brought together ten research partners and two poultry breeders, from different European countries (Germany, Belgium, Spain, France, Great Britain, Sweden) and Canada, between 2001 and 2004. Yves Nys, the French project leader from the INRA Research Centre in Tours, was the project coordinator.
2 Scientific contact:
Yves Nys
Tel.: +33 (0)2 47 42 78 43 or +33 (0)2 47 42 78 51
e-mail: yves.nys@tours.inra.fr
Poultry Research Unit,
Animal Physiology and Livestock Systems and Animal Genetics Departments,
Tours Research Centre
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Written by :
INRA press service, phone: +33 (0)1 42 75 91 69
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