Abstract
BackgroundEggshell is subject to quality loss with aging process of laying hens, and damaged eggshells result in economic losses of eggs. However, the genetic architecture underlying the dynamic eggshell quality remains elusive. Here, we measured eggshell quality traits, including eggshell weight (ESW), eggshell thickness (EST) and eggshell strength (ESS) at 11 time points from onset of laying to 72 weeks of age and conducted comprehensive genome-wide association studies (GWAS) in 1534 F2 hens derived from reciprocal crosses between White Leghorn (WL) and Dongxiang chickens (DX).ResultsESWs at all ages exhibited moderate SNP-based heritability estimates (0.30 ~ 0.46), while the estimates for EST (0.21 ~ 0.31) and ESS (0.20 ~ 0.27) were relatively low. Eleven independent univariate genome-wide screens for each trait totally identified 1059, 1026 and 1356 significant associations with ESW, EST and ESS, respectively. Most significant loci were in a region spanning from 57.3 to 71.4 Mb of chromosome 1 (GGA1), which together account for 8.4 ~ 16.5 % of the phenotypic variance for ESW from 32 to 72 weeks of age, 4.1 ~ 6.9 % and 2.95 ~ 16.1 % for EST and ESS from 40 to 72 weeks of age. According to linkage disequilibrium (LD) and conditional analysis, the significant SNPs in this region were in extremely strong linkage disequilibrium status. Ultimately, two missense SNPs in GGA1 and one in GGA4 were considered as promising loci on three independent genes including ITPR2, PIK3C2G, and NCAPG. The homozygotes of advantageously effective alleles on PIK3C2G and ITPR2 possessed the best eggshell quality and could partly counteract the negative effect of aging process. NCAPG had certain effect on eggshell quality for young hens.ConclusionsIdentification of the promising region as well as potential candidate genes will greatly advance our understanding of the genetic basis underlying dynamic eggshell quality and has the practical significance in breeding program for the improvement of eggshell quality, especially at the later part of laying cycle.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1795-7) contains supplementary material, which is available to authorized users.
Highlights
Eggshell is subject to quality loss with aging process of laying hens, and damaged eggshells result in economic losses of eggs
Phenotype description and genetic parameters Means and standard deviations for eggshell quality traits, including eggshell weight (ESW), eggshell thickness (EST) and eggshell strength (ESS), at 11 time points from onset of laying to 72 weeks of age are presented in Table 1 and Additional file 1: Figure S1
These three eggshell quality traits displayed a smooth curve with hen age except 36 weeks-old, at which ESW, EST and ESS showed a abrupt decrease (Additional file 1: Figure S1) and the results of Genome-wide Association (GWA) analysis in this week were unusual (Table 3)
Summary
Eggshell is subject to quality loss with aging process of laying hens, and damaged eggshells result in economic losses of eggs. The genetic architecture underlying the dynamic eggshell quality remains elusive. Low eggshell quality will lead to more cracked eggs in the automatic sorting and packing process in the modern egg industrial production [4]. It has been estimated that improving the mean eggshell strength by one Newton will lead to 0.5 % less broken eggs per hen per laying cycle [5]. Eggshell are subject to quality loss with the aging process of laying hens [9], which hinders the developmental trend to prolong the laying cycles of egg-type chicken in the future. Understanding the genetic control for dynamic eggshell quality with aging process is of great economic and biological importance
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