Genetics of egg quality

Abstract

Egg quality has gained importance in genetic improvement of laying hens. Egg weight, eggshell thickness (either directly or indirec-tly recorded), yolk proportion and egg albumen quality (Haugh units) exhibit moderate to high heritability values (0.30 to 0.60) but egg weight is negatively correlated with egg number. Combining within-line selection with crossbreeding has resulted in an increase in the number of eggs with a constant and rather high egg weight (62g on average). Moreover, experimental selection and exploration of genetic diversity, have given access to new genetic variability, in chickens and quails, of egg shell colour, yolk proportion and lipid composition of the yolk. Yet, the genes controlling egg laying traits and technological qualities of the egg are still poorly known. QTL controlling a significant part of genetic variability were identified in fowl and quail. Recently, major genes were identified, such as a mutation of the FMO3 enzyme responsible for the fishy taint of eggs when the hen is fed with rapeseed. Numerous studies are focussed on microbial quality of eggs, with a priority to the study of the salmonella carrier state, where the effects of several genes have been identified (SLC11A1, TLR4).