BackgroundUniformity of eggs is an important aspect for retailers because consumers prefer homogeneous products. One of these characteristics is the color of the eggshell, especially for brown eggs. Existence of a genetic component in environmental variance would enable selection for uniformity of eggshell color. Therefore, the objective of this study was to quantify the genetic variance in environmental variance of eggshell color in purebred and crossbred laying hens, to estimate the genetic correlation between environmental variance of eggshell color in purebred and crossbred laying hens and to estimate genetic correlations between environmental variance at different times of the laying period.MethodsWe analyzed 167,651 and 79,345 eggshell color records of purebred and crossbred laying hens, respectively. The purebred and crossbred laying hens originated mostly from the same sires. Since eggshell color records of crossbred laying hens were collected per cage, these records could be related only to cage and sire family. A double hierarchical generalized linear sire model was used to estimate the genetic variance of the mean of eggshell color and its environmental variance. Approximate standard errors for heritability and the genetic coefficient of variation for environmental variance were derived.ResultsThe genetic variance in environmental variance at the log scale was equal to 0.077 and 0.067, for purebred and crossbred laying hens, respectively. The genetic coefficient of variation for environmental variance was equal to 0.28 and 0.26, for purebred and crossbred laying hens, respectively. A genetic correlation of 0.70 was found between purebred and crossbred environmental variance of eggshell color, which indicates that there is some reranking of sires for environmental variance of eggshell color in purebred and crossbred laying hens. Genetic correlations between environmental variance of eggshell color in different laying periods were generally higher than 0.85, except between early laying and mid or late laying periods.ConclusionsOur results indicate that genetic selection can be efficient to improve uniformity of eggshell color in purebreds and crossbreds, ideally by applying combined crossbred and purebred selection. This methodology can be used to estimate genetic correlations between purebred and crossbred lines for uniformity of other traits and species.Electronic supplementary materialThe online version of this article (doi:10.1186/s12711-016-0212-2) contains supplementary material, which is available to authorized users.

La sélection des pondeuses commerciales repose sur un ensemble de critères où les paramètres de qualité de l’œuf prennent une importance croissante. Les caractères tels que le poids de l’œuf, la solidité de coquille (mesurée directement ou indirectement) la proportion de jaune et la qualité du blanc (unités Haugh) présentent une assez forte variabilité génétique (héritabilité de 0,30 à 0,60). Malgré une corrélation négative entre le poids d’œuf et le nombre d’œufs, la combinaison de la sélection en lignée pure et du croisement a permis d’améliorer le nombre d’œufs tout en stabilisant le poids d’œuf à un niveau élevé (62 g en moyenne). La variabilité génétique de la couleur de coquille, de la proportion de jaune et de la composition en lipides du jaune a été explorée, chez la poule comme chez la caille, par la sélection expérimentale et l’étude de races locales. Cependant, les gènes contrôlant les caractères de ponte et de la qualité technologique de l’œuf sont encore mal connus. Quelques protocoles de détection de QTL ont permis d’identifier des régions chromosomiques contrôlant une part significative de la variabilité de ces caractères, chez la poule et la caille. Récemment des gènes majeurs ont été identifiés comme l’enzyme FMO3 responsable de l’odeur de poisson d’œufs de poule nourries au tourteau de soja. De nombreuses études portent sur la la qualité bactériologique des oeufs, avec une priorité donnée au portage de salmonelles, pour laquelle plusieurs gènes ont été identifiés (SLC11A1, TLR4). Ces perspectives sont encourageantes pour répondre aux demandes croissantes du consommateur en matière de qualité des produits.

Exposure of laying hens to chronic heat stress results in loss of egg production. It should be possible to improve hen resilience to chronic heat stress by genetic selection but measuring their sensitivity through internal temperature is time consuming and is not very precise. In this study we used infrared thermography to measure the hen's capacity to dissipate heat, in a commercial line of laying hens subjected to cycles of neutral (N, 19.6°C) or high (H, 28.4°C) ambient temperatures. Mean body temperatures (BT) were estimated from 9355 infrared images of wing, comb and shank taken from 1200 hens. Genetic parameters were estimated separately for N and H temperatures. Correlations between BT and plumage condition were also investigated. Wing temperature had low heritability (0.00 to 0.09), consistent with the fact that wing temperature mainly reflects the environmental temperature and is not a zone of heat dissipation. The heritability of comb temperature was higher, from 0.15 to 0.19 in N and H conditions, respectively. Finally, the shank temperature provided the highest heritability estimates, with values of 0.20 to 0.22 in H and N conditions, respectively. Taken together, these results show that heat dissipation is partly under genetic control. Interestingly, the genetic correlation between plumage condition and shank and comb temperatures indicated that birds with poor condition plumage also had the possibility to dissipate heat through featherless areas. Genetic correlations of temperature measurements with egg quality showed that temperatures were correlated with egg width and weight, yolk brightness and yellowness and Haugh units only under H conditions. In contrast, shell colour was correlated with leg temperature only at thermo-neutrality.