Abstract
Availability of the complete genome sequence as well as high-density SNP genotyping platforms allows genome-wide association studies (GWAS) in chickens. A high-density SNP array containing 57,636 markers was employed herein to identify associated variants underlying egg production and quality traits within two lines of chickens, i.e., White Leghorn and brown-egg dwarf layers. For each individual, age at first egg (AFE), first egg weight (FEW), and number of eggs (EN) from 21 to 56 weeks of age were recorded, and egg quality traits including egg weight (EW), eggshell weight (ESW), yolk weight (YW), eggshell thickness (EST), eggshell strength (ESS), albumen height(AH) and Haugh unit(HU) were measured at 40 and 60 weeks of age. A total of 385 White Leghorn females and 361 brown-egg dwarf dams were selected to be genotyped. The genome-wide scan revealed 8 SNPs showing genome-wise significant (P<1.51E-06, Bonferroni correction) association with egg production and quality traits under the Fisher's combined probability method. Some significant SNPs are located in known genes including GRB14 and GALNT1 that can impact development and function of ovary, but more are located in genes with unclear functions in layers, and need to be studied further. Many chromosome-wise significant SNPs were also detected in this study and some of them are located in previously reported QTL regions. Most of loci detected in this study are novel and the follow-up replication studies may be needed to further confirm the functional significance for these newly identified SNPs.
Highlights
Modern egg layers have been selected for egg production and quality for decades
66 QTL were associated with 7 types of egg production traits including egg production rate, age at first egg, the number of eggs and so on, and 223 QTL were associated with 38 types of egg quality traits such as egg shell thickness, egg shell strength and yolk weight
As egg weight has a great impact on eggshell and yolk weight, it was taken as a covariant in the association test for eggshell weight (ESW) and YW
Summary
Modern egg layers have been selected for egg production and quality for decades. A breeding program for egg-type chickens has to face two major problems, the measurement of phenotypic data for individual hens and the efficient selection of cockerels which do not have records on laying performance and egg quality. Great success has been achieved in layer breeding over the past decades, it is becoming more and more difficult with traditional breeding programs to make improvement in egg production and quality traits. With advances in technologies of molecular genetics and availability of DNA markers, identifying QTL controlling egg production and quality traits for application in marker-assisted selection has been progressing rapidly [1,2].
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