The poultry industry relies on artificial incubation of eggs to prevent the transfer of micro organisms from one generation to the next. Despite this the vertical transmission from broiler and layer breeders to production flocks has been identified by the European food safety agency as the most likely route of transfer of antibiotic resistant e-coli and salmonella. There is also the opportunity for horizontal transmission to occur during the collection and transport of eggs. Irrespective of the route or site of transfer, the entry of pathogenic or zoonotic organisms to the egg contents is undesirable for food safety, animal and human health.
The cuticle is a protein layer which covers the surface of the egg and fills the gas exchange pores. The cuticle forms the first line of defence to the penetration of bacteria derived both from vertical transmission in the cloaca (where the egg and faeces exit the chicken) and horizontal transmission from the environment e.g. contact with collecting belts or handling equipment. In preliminary studies we have been able for the first time to quantify the cuticle cover on eggs using a relatively cumbersome two-stage process and estimate the importance of genetics for of this trait (heritability, 0.27). This suggested that the trait has good potential for genetic selection. We also have evidence that the natural variation in cuticle coverage is responsible for differences in the ability of bacteria to penetrate the egg. This demonstrated that eggs with good cuticle quality were never penetrated by E. coli whereas eggs with poor cuticle quality were frequently penetrated.
In this study we will address the physiochemical, physiological and genetic parameters that characterise the cuticle and use this information to develop a simple one step measurement tool for cuticle assessment using the intrinsic autofluorescence of the cuticle. Both the amount and the degree to which the proteins are modified by the addition of sugar residues (glycosylation) will be quantified. In the first instance this will be achieved using a matrix of wavelengths of light both shone on and emitted from the egg surface. This will allow the optimal wavelengths to be selected which can distinguish cuticle from potential interfering substances such as feather debris or pigment and a simple to use measurement tool built.
The amount of modification of the cuticle proteins by sugar residues will be assessed by how they change the rate at which the emission of light occurs. Both the measurements will be used to estimate reliably the genetic contribution to variation in cuticle coverage in meat and egg laying strains of poultry and to determine genetic correlations with important production parameters to ensure there are no major negative consequences. As well as the contribution of genetics to variation in the trait, we will measure the contribution of environmental influences such as stress, age and how the hormones involved in the expulsion of the egg control cuticle deposition. In the project we will also further characterise how cuticle and its degree of modification by sugars acts both as a physical and a chemical barrier to bacteria and extend our understanding of the genes involved with cuticle formation and their expression.
Overall this will provide the information required to allow accurate genetic selection for improved cuticle coverage to reduce the risk of pathogens entering the egg. We will also gain fundamental knowledge about the biological mechanisms which give rise to the cuticle and its role as a physical and chemical barrier to microbial penetratio