Posted: August 26th, 2010 - 7:22am

Improving egg safety through genetics
In this project a combination of approaches have increased our understanding of the genetics and physiology of the formation of the eggshell. We have delivered a number of tangible tests and assays which will contribute directly to genetic improvement of egg quality and hence safety.
Why eggshell quality?
To the consumer eggs are an excellent balanced source of nutrition and are widely accepted. However, poor eggshell quality leads to increased numbers of cracked or damaged eggs. Cracked eggs encourage bacterial infections and are 3 to 93 times more likely to cause Salmonella outbreaks than intact eggs. If there were 10% fewer cases of human Salmonella infection across the EU it would save about €400milion per year. The egg shell is also critical to the consumers’ impression of the product. Cracked and or damaged shells as well as increasing risk from pathogens harm the image of the product. To the breeder and farmer of laying hens, egg quality is one of the primary concerns. Egg quality is important to the breeder and farmer for the reasons it is important to the consumer and because good egg quality contributes to the profitability of the commercial hen and to its marketability. Egg breakage causes significant waste directly but most importantly it reduces the lifespan of laying hens. Increases in the period over which flock egg quality remains high would have impressive effects in environmental impact over the life cycle of production.
Research goals and results
The project sought to both better measure aspects of shell quality which contribute to its safety and to identify genetic markers which are associated with existing measurements of egg quality. We also identified genes expressed in the shell gland, the structure where the egg is formed, to understand this process better and to compare with the chromosomal location of the genetic markers.
Measurement tools
The cuticle is protective coating which prevents bacterial penetration through the gas exchange pores in the egg shell. It has never been quantified. A method was established using dyes and reflectrometry which allowed us to establish that the degree of cuticle coverage was moderately determined by the genetics of the hen that laid it. We also established that the variation observed in the cuticle was correlated with bacterial penetration of the shell. The egg shell is predominately composed of calcium carbonate crystals. Crystal size determines the properties of materials so we determined size using X-ray diffraction. It turned out that crystal size is highly dependent on genetics of the hen that laid it. Crystal size appears to be an important component of determining the shell thickness which is a major part of shell strength.
Genetic markers
By using crosses between commercial pure line hens we identified regions of the genome that controlled shell strength on chromosome 2, 3 6 14 and Z which were then densely genotyped using SNPs. The SNPs with the highest significance values were tested on pure line hens and found to have significant associations with shell quality traits. This means that pure line hens can be selected using these markers.
Genes involved in shell formation
Large scale transcriptomic studies have identified many of the transporter molecules responsible for the prodigious secretion of proteins and minerals required for shell formation.
Sustainable breeding
We have developed new tools to measure aspects of egg shell structure which underlie egg safety and quality and molecular tools to improve the efficiency of selection. This will allow breeders to select hens that lay better and healthier eggs.