Genetic variation in eggshell crystal size and orientation is large and these traits are correlated with shell thickness and are associated with eggshell matrix protein markers

Abstract

SummaryThe size and orientation of calcium carbonate crystals influence the structure and strength of the eggshells of chickens. In this study, estimates of heritability were found to be high (0.6) for crystal size and moderate (0.3) for crystal orientation. There was a strong positive correlation (0.65) for crystal size and orientation with the thickness of the shell and, in particular, with the thickness of the mammillary layer. Correlations with shell breaking strength were positive but with a high standard error. This was contrary to expectations, as in man‐made materials smaller crystals would be stronger. We believe the results of this study support the hypothesis that the structural organization of shell, and in particular the mammillary layer, is influenced by crystal size and orientation, especially during the initial phase of calcification. Genetic associations for crystal measurements were observed between haplotype blocks or individual markers for a number of eggshell matrix proteins. Ovalbumin and ovotransferrin (LTF) markers for example were associated with crystal size, while ovocleidin‐116 and ovocalyxin‐32 (RARRES1) markers were associated with crystal orientation. The location of these proteins in the eggshell is consistent with different phases of the shell‐formation process. In conclusion, the variability of crystal size, and to a lesser extent orientation, appears to have a large genetic component, and the formation of calcite crystals are intimately related to the ultrastructure of the eggshell. Moreover, this study also provides evidence that proteins in the shell influence the variability of crystal traits and, in turn, the shell’s thickness profile. The crystal measurements and/or the associated genetic markers may therefore prove to be useful in selection programs to improve eggshell quality.

Egg quality and age of laying hens: implications for product safety

“…The steady reduction in albumen quality with increased flock age has also been reported by several researchers (Williams 1992;Silversides 1994). The heritability of many egg quality parameters is high (Dunn 2011;Dunn et al 2012), which means that genetic selection by major breeding companies can assist with improvements in quality, in addition to management improvements. The use of MST cuticle blue stain for determining the extent of cuticle cover in avian egg shells has been verified by correlating the extent of staining with the appearance of the shell cuticle under the scanning electron microscope.…”

Quantitative proteomics provides new insights into chicken eggshell matrix protein functions during the primary events of mineralisation and the active calcification phase

“…stage (26 th most abundant protein, Figure 5C). Different studies in vivo demonstrated correlations between ovocalyxin-32 (OCX32) gene polymorphism and different eggshell quality phenotypes, such as eggshell strength or mammillary layer thickness [73][74][75][76][77], which support its involvement in the control of the crystal texture of the eggshell. Its overabundance at 7 hours p.o.…”

A Review of the Fossil Record of Turtle Reproduction: Eggs, Embryos, Nests and Copulating Pairs

“…The chorioallantoic membrane provides a direct connection between the embryo and the egg, which allows for aerobic metabolism and the uptake of calcium by the embryo from the eggshell (Carpenter 1999). In addition, the aragonite structure of the eggshell is under direct genetic control (Rodriguez-Navarro et al 2007;Dunn et al 2012), and the embryo, yolk, albumin, membranes and mineralized eggshell form a single unit. As such, fossil eggs and eggshell offer insight into some of the earliest ontogenetic stages of extinct organisms and are occasionally augmented by data from identifiable embryonic remains and gravid females.…”