Genetic variation and potential for genetic improvement of cuticle deposition on chicken eggs

Abstract

Background The cuticle is an invisible glycosylated protein layer that covers the outside of the eggshell and forms a barrier to the transmission of microorganisms. Cuticle-specific staining and in situ absorbance measurements have been used to quantify cuticle deposition in several pure breeds of chicken. For brown eggs, a pre-stain and a post-stain absorbance measurement is required to correct for intrinsic absorption by the natural pigment. For white eggs, a post-stain absorbance measurement alone is sufficient to estimate cuticle deposition. The objective of the research was to estimate genetic parameters and provide data to promote adoption of the technique to increase cuticle deposition and reduce vertical transmission of microorganisms. Results For all pure breeds examined here, i.e. Rhode Island Red, two White Leghorns, White Rock and a broiler breed, the estimate of heritability for cuticle deposition from a meta-analysis was moderately high (0.38 ± 0.04). In the Rhode Island Red breed, the estimate of the genetic correlation between measurements recorded at early and late times during the egg-laying period was ~ 1. There was no negative genetic correlation between cuticle deposition and production traits. Estimates of the genetic correlation of cuticle deposition with shell color ranged from negative values or 0 in brown-egg layers to positive values in white- or tinted-egg layers. Using the intrinsic fluorescence of tryptophan in the cuticle proteins to quantify the amount of cuticle deposition failed because of complex quenching processes. Tryptophan fluorescence intensity at 330 nm was moderately heritable, but there was no evidence of a non-zero genetic correlation with cuticle deposition. This was complicated furthermore by a negative genetic correlation of fluorescence with color in brown eggs, due to the quenching of tryptophan fluorescence by energy transfer to protoporphyrin pigment. We also confirmed that removal of the cuticle increased reflection of ultraviolet wavelengths from the egg. Conclusions These results provide additional evidence for the need to incorporate cuticle deposition into breeding programs of egg- and meat-type birds in order to reduce vertical and horizontal transmission of potentially pathogenic organisms and to help improve biosecurity in poultry. Electronic supplementary material The online version of this article (10.1186/s12711-019-0467-5) contains supplementary material, which is available to authorized users.

Transcriptome analysis of the uterus of hens laying eggs differing in cuticle deposition

“…We also demonstrated on multiple lines of divergent breeds of chicken that the quantity of cuticle is a heritable trait and the hen's level of cuticle deposition on eggs was remarkably constant through its life [10,18]. Most importantly, the quantity of cuticle had a significant effect on bacterial penetration of eggs [8,10,19].…”

“…A further aspect of this study was to compare the uterus transcriptome from the extremes of the population distribution for the trait. A photograph of what the extremes of the cuticle deposition distribution look like is available in the supplemental material of a recent paper along with the associated the genetic parameters of the trait [18]. Hens at the low end of the distribution have virtually no cuticle whilst those at the top have a strong even cuticle deposition resulting in a large numerical difference in cuticle reflectance between the eggs laid by the hens that were used for transcriptome analysis.…”

“…Hens were reared in cages in an environmentally controlled poultry house, receiving 16 h of light per day and were fed following standard commercial practice. Hens were selected based on measurements made at 31 and 50 weeks of age [18]. Genetic correlations across age for the trait of cuticle deposition was near 1 [18] suggesting hens that were laying good or poor cuticle covered eggs earlier in life would continue to do so and indeed that was the case.…”

“…Hens were selected based on measurements made at 31 and 50 weeks of age [18]. Genetic correlations across age for the trait of cuticle deposition was near 1 [18] suggesting hens that were laying good or poor cuticle covered eggs earlier in life would continue to do so and indeed that was the case. Nonetheless, two eggs from each hen were measured to ensure the hens were still laying eggs with good or poor cuticle.…”

“…These factors would affect the overall quality of the cuticle and the expression of genes which control this, these factors might include the receptors for ovarian steroids [ 15 ] and growth factors thought to interact with them [ 16 , 17 ]. We also demonstrated on multiple lines of divergent breeds of chicken that the quantity of cuticle is a heritable trait and the hen’s level of cuticle deposition on eggs was remarkably constant through its life [ 10 , 18 ]. Most importantly, the quantity of cuticle had a significant effect on bacterial penetration of eggs [ 8 , 10 , 19 ].…”