Abstract
BackgroundThe 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.ResultsFor 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.ConclusionsThese 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.
Highlights
The cuticle is an invisible glycosylated protein layer that covers the outside of the eggshell and forms a barrier to the transmission of microorganisms
Breed 1 Hens for breed 1 originated from a single generation of the Rhode Island Red (RIR) breed, which is a pure breed laying brown eggs and a contributor to the male that was used to produce the Lohmann Brown commercial layers (Lohmann Tierzucht GmbH, Germany)
For tinted broiler eggs, we found that a single post-stain measurement had a large enough genetic correlation with cuticle deposition to obtain satisfactory results, since, for broilers, correlated changes in color are of no economic value
Summary
The cuticle is an invisible glycosylated protein layer that covers the outside of the eggshell and forms a barrier to the transmission of microorganisms. For a functional application, we observed that within the normal range of variation in cuticle deposition, there was a significant effect on bacterial penetration of eggs [3, 4], with bacteria almost never penetrating eggs that had the most cuticle deposition, whereas those with a poor cuticle were frequently penetrated We extended these studies to include more breeds of chicken (layers and broilers) and strains of bacteria [3] and obtained results that are consistent with the observation that complete removal of the cuticle increases both water and particle penetration [10, 11]
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