Concentration of egg white antimicrobial and immunomodulatory proteins is related to eggshell pigmentation across traditional chicken breeds

Influence of the genotype of the hen (Gallus gallus domesticus) on main parameters of egg quality, chemical composition of the eggs under uniform environmental conditions

The objective of this study was to identify and compare the quality characteristics and concentrations of various compounds in eggs from several pure breeds and lines of hens reared under the same environmental conditions and fed a commercial feed. A total of 280 hens aged 52 to 56 wk belonging to 14 different breeds or lines of hens worldwide were included in this study. Their eggs were characterized by wide differences in various egg quality parameters. Breeds and lines of hens with a higher lutein content in eggs were characterized by a lower beta-carotene content (e.g. Hy line brown, Cochin miniature, Ayam Cemani) (P < 0.001). Additionally, vitamin D, cholesterol, and fatty acid contents were also different between eggs, from 1.51 to 1.79 μg/100g; from 14.1 to 15.4 mg/g fat, PUFA from 19.6 to 22.8 g/100g fat, and SFA from 32.8 to 37.8 g/100g fat respectively (P < 0.001). Lysozyme content also exhibited significant variation among breeds, with some showing a 2-fold higher content in eggs compared to others (0.31% - cochin miniature, 0.66% Faverolle) (P < 0.001). Our study demonstrated that intensively selected hen breeds like Hy-line Brown Hybrid had an improved egg quality seen by the increase in many parameters (e.g., egg weight, Haugh unit, Lutein, vitamins D, MUFA) compared to pure breed hens. In conclusion, genetic differences between breeds and lines of hens have a significant impact on the quality of eggs.

Physicochemical Index Analyses of the Egg White in Blue-Shelled Eggs and Commercial Brown-Shelled Eggs during Storage

To compare the physical and chemical changes in egg whites during storage, assisting in the evaluation of differences in egg freshness between various chicken breeds, we chose 240 blue-shelled eggs (Blue group) and 240 commercial brown-shelled eggs (Brown group) that 28-week-old hens had laid. In this study, all eggs were stored at 25 °C. The egg weight, egg components' weight and proportion, Haugh Unit value and the contents of S-ovalbumin, ovomucin and lysozyme in the thick albumen (KA) and thin albumen (NA) were measured at eight time points every 3 days until the 21st day of storage. The eggshell, yolk and KA proportions in the Brown group were significantly lower, whereas the NA proportion was significantly higher than that in the Blue group (p < 0.001). The Haugh Unit value and S-ovalbumin in the Brown group were significantly higher, whereas KA ovomucin and NA lysozyme were significantly lower than those in the Blue group (p < 0.001). There existed significant negative correlations between the KA and NA, irrespective of weight or proportion. The Haugh Unit value was significantly positively correlated with lysozyme and ovomucin, but significantly negatively correlated with S-ovalbumin. During storage, the KA weight (proportion), Haugh Unit value, lysozyme and ovomucin decreased, whereas the NA weight (proportion) and S-ovalbumin increased. At each time point, the NA lysozyme in the Brown group was lower than that in the Blue group (p < 0.05). After storage for 6 days, the KA ovomucin in the Brown group began to be lower than that in the Blue group (p < 0.05). The study showed that the weight (proportion) differences in egg components between blue-shelled eggs and commercial brown-shelled eggs are mainly due to the NA. The Haugh Unit value and albumin protein indexes of blue-shelled eggs were better than those of brown-shelled eggs, and showed mild changes during storage, indicating the better storage performance of blue-shelled eggs.

Transcriptome and histological analyses on the uterus of freckle egg laying hens

BACKGROUND

In this study, we explored the characteristics and causes of freckle formation. We collected 15 normal and freckled eggs each for eggshell index testing and hypothesized that the structure and function of the uterus would have a direct effect on freckled egg production given that eggshells are formed in the uterus. To test this hypothesis, we collected uterine tissue from laying hens (418 days of age) that laid normal (Group C, n = 13) and freckled (Group T, n = 16) eggs for 7 consecutive days.

RESULTS

When we examined the eggshell quality, we found that the L value was significantly lower (P < 0.05) in the freckled site group of freckled eggs compared to the normal egg group during the detection of blunt pole, equator, and sharp pole of the eggshell color. The a-values of the three positions were significantly higher (P < 0.05) in the freckled site group of freckled eggs, and the a-values of the blunt pole were significantly lower (P < 0.05) in the background site group of freckled eggs, compared to the normal egg group. The b-values were significantly higher (P < 0.05) at three locations in the freckled site group of freckled eggs compared to the normal egg group. During the detection of eggshell thickness, the blunt pole was significantly higher (P < 0.05) in the freckled egg site group of freckled eggs compared to the normal egg group, and there was no significant difference between the other groups (P > 0.05). There was no significant difference (P > 0.05) between the transverse and longitudinal diameters of the eggs in each group.We then performed histopathology and transcriptome analyses on the collected tissue. When compared with group C, uterine junctional epithelial cells in group T showed significant defects and cilia loss, and epithelial tissue was poorly intact. From transcriptomics, genes that met (|log2FC|) ≥ 1 and P < 0.05 criteria were screened as differentially expressed genes (DEGs). We identified a total of 136 DEGs, with 101 up- and 35 down-regulated genes from our RNA-seq data. DEGs identified by enrichment analyses, which were potentially associated with freckled egg production were: IFI6, CCL19, AvBD10, AvBD11, S100A12, POMC, and UCN3. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses showed that pathways were associated with immunoreaction and stress stimulation, e.g., complement activation, interleukin-1 cell reactions, viral responses, cell reactions stimulated by corticotropin releasing hormone, steroid hormone mediated signaling pathways, staphylococcal infections, B cell receptor signaling pathways, and natural killer cell mediated cytotoxicity.

CONCLUSIONS

From these data, freckled areas deepen freckled eggshell color, but background areas are not affected. At the same time,we reasoned that freckle eggs may result from abnormal immune responses and impaired uterine functions induced by stress. Therefore, the uterus of laying hens in a state of stress and abnormal immune function can cause the appearance of freckled eggs.

Transcriptome profiling analysis of uterus during chicken laying periods

The avian eggshell is formed in the uterus. Changes in uterine function may have a significant effect on eggshell quality. To identify the vital genes impacting uterine functional maintenance in the chicken, uteri in three different periods (22W, 31W, 51W) were selected for RNA sequencing and bioinformatics analysis. In our study, 520, 706 and 736 differentially expressed genes (DEGs) were respectively detected in the W31 vs W22 group, W51 vs W31 group and W51 vs W22 group. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated DEGs were enriched in the extracellular matrix, extracellular region part, extracellular region, extracellular matrix structural constituent, ECM receptor interaction, collagen-containing extracellular matrix and collagen trimer in the uterus (P < 0.05). Protein-protein interaction analysis revealed that FN1, LOX, THBS2, COL1A1, COL1A2, COL5A1, COL5A2, POSTN, MMP13, VANGL2, RAD54B, SPP1, SDC1, BTC, ANGPTL3 might be key candidate genes for uterine functional maintenance in chicken. This study discovered dominant genes and pathways which enhanced our knowledge of chicken uterine functional maintenance.

Effect of Hen Genotype and Laying Time on Egg Quality and Albumen Lysozyme Content and Activity

According to research, egg quality and lysozyme content are influenced by a number of factors, which are mostly known in the case of commercial hybrids, while in breeds included in genetic resources conservation programmes, new research results in this regard are emerging. The aim of the study was to determine the effect of egg laying time and genotype of selected Polish native breeds of hens on egg quality and lysozyme content and activity in the albumen. The study material consisted of eggs collected from four strains of laying hens included in the Polish conservation programme, i.e., Green-legged Partridge (Z-11), Yellow-legged Partridge (Ż-33), Rhode Island Red (R-11) and Leghorn (H-22). At week 56, 28 eggs were randomly collected at 7:00 and 13:00 h from each breed of hen and assessed for quality. Laying time influenced certain egg quality traits. Eggs laid by hens in the morning were characterised by 1.7 g lower total weight and albumen weight, 2.4 pores/cm² higher number of shell pores, 0.15 higher albumen pH values and 0.17 lower yolk pH values compared to those laid in the morning. The time of laying did not affect the level and activity of lysozyme in the albumen. A significant negative correlation was found between eggshell traits and albumen height, and between Haugh unit and lysozyme content and activity in the albumen. The studied egg quality traits were more influenced by genotype than by the egg-laying time.

New insights into the relationships between egg maternal components: the interplays between albumen steroid hormones, proteins and eggshell protoporphyrin

Recent studies have shown that the egg yolk maternal components, which are a mixture of substances that can affect the developing embryo, do not act separately but are interconnected and co-adapted. Surprisingly, no study to date has focused on the associations between maternally derived albumen steroids and albumen and eggshell compounds with pleiotropic effects. Eggshell pigment protoporphyrin (PROTO IX) should provide primary antimicrobial protection for eggs, but as a proven pro-oxidant, it may compromise female fitness. Abundant albumen proteins ovotransferrin (OVOTR) and lysozyme (LSM) have been shown to have antimicrobial, antioxidant, immunoregulatory and growth-regulatory roles. To investigate associations between albumen steroids and OVOTR, LSM and eggshell cuticle PROTO IX, we used chicken eggs with differently pigmented eggshells. We found that albumen steroid hormones were strongly intercorrelated. In addition, we revealed that albumen LSM and testosterone (T) were positively associated, while a negative association was found between albumen LSM and pregnenolone (P5). Eggshell cuticle PROTO IX was negatively associated with the concentration of albumen 17α-hydroxypregnenolone (17-OHP5). Finally, of all the hormones tested, only the concentration of albumen 17-OHP5 correlated negatively with egg volume and varied with eggshell colour and chicken breed. Although experimental evidence for the effect of maternal albumen steroids on avian developing embryo is still scarce, our study is the first to highlight co-variation and potential co-adjustment of maternally derived albumen steroids, proteins and eggshell cuticle pigment suggesting similar allocation mechanisms known for yolk maternal compounds with the potential to influence the avian embryo and offspring phenotype.

Extraction of Lysozyme from Chicken Albumen Using Polyelectrolyte Complexes

Cells use droplet-like membrane-less organelles (MLOs) to compartmentalize and selectively take-up molecules, such as proteins, from their internal environment. These membraneless organelles can be mimicked by polyelectrolyte complexes (PECs) consisting of oppositely charged polyelectrolytes. Previous research has demonstrated that protein uptake strongly depends on the PEC composition. This suggests that PECs can be used to selectively extract proteins from a multi-protein mixture. With this in mind, the partitioning of the protein lysozyme in four PEC systems consisting of different weak and strong polyelectrolyte combinations is investigated. All systems show similar trends in lysozyme partitioning as a function of the complex composition. The release of lysozyme from complexes at their optimal lysozyme uptake composition is investigated by increasing the salt concentration to 500 mm NaCl or lowering the pH from 7 to 4. Complexes of poly(allylamine hydrochloride) and poly(acrylic acid) have the best uptake and release properties. These are used for selective extraction of lysozyme from a hen-egg white protein matrix. The (back)-extracted lysozyme retains its enzymatic activity, showing the capability of PECs to function as extraction media for proteins.

To culture or not to culture: careful assessment of metabarcoding data is necessary when evaluating the microbiota of a modified-atmosphere-packaged vegetarian meat alternative throughout its shelf-life period

Background

As the increased consumption of ready-to-eat meat alternatives is a fairly recent trend, little is known about the composition and dynamics of the microbiota present on such products. Such information is nonetheless valuable in view of spoilage and food safety prevention. Even though refrigeration and modified-atmosphere-packaging (MAP) can extend the shelf-life period, microbial spoilage can still occur in these products. In the present study, the microbiota of a vegetarian alternative to poultry-based charcuterie was investigated during storage, contrasting the use of a culture-dependent method to a culture-independent metagenetic method.

Results

The former revealed that lactic acid bacteria (LAB) were the most abundant microbial group, specifically at the end of the shelf-life period, whereby Latilactobacillus sakei was the most abundant species. Metabarcoding analysis, in contrast, revealed that DNA of Xanthomonas was most prominently present, which likely was an artifact due to the presence of xanthan gum as an ingredient, followed by Streptococcus and Weissella.

Conclusions

Taken together, these results indicated that Lb. sakei was likely the most prominent specific spoilage organisms (SSO) and, additionally, that the use of metagenetic analysis needs to be interpreted with care in this specific type of product. In order to improve the performance of metagenetics in food samples with a high DNA matrix but a low bacterial DNA load, selective depletion techniques for matrix DNA could be explored.

Effect of Laying Hen Genotype, Age and Some Interior Egg Quality Traits on Lysozyme Content

The objective of the study was to evaluate the quality of eggs laid by native breed hens of different ages (33 and 53 weeks of age), with particular consideration of the lysozyme parameters. Eggs were collected from 6 breeds/strains of laying hens under the genetic resources conservation in Poland, i.e. Greenleg Partridge (Z-11), Yellowleg Partridge (Ż-33), Rhode Island Red (R-11), Rhode Island White (A-33), Sussex (S-66) and Leghorn (H-22). The yolks of eggs from older hens had a more favourable, intense colour, but the freshness parameters (albumen height and Haugh units) of these eggs were lower. The albumen of eggs from older hens showed greater content and higher enzymatic activity of lysozyme in both thin and thick albumen. Among the six strains of hens, lysozyme content and enzymatic activity were highest in the egg albumen of strains Ż-33, Z-11 and R-11, and lowest in that of strain H-22. The analysed eggs showed statistically significant correlations between some interior egg quality traits (albumen weight, albumen height, Haugh units, yolk colour) and the discussed enzyme parameters. These traits are influenced by genotype and age of the hens.

Mechanisms associated with the depigmentation of brown eggshells: a review

Eggshell color is an important shell quality trait that influences consumer preference. It is also of particular importance with respect to sexual signaling and the physiological and mechanical properties of shell pigment. Pigments include protoporphyrin IX, biliverdin, and traces of biliverdin zinc chelates, with brown eggs being notably rich in protoporphyrin IX, the synthesis of which has a marked effect on the intensity of brown eggshell color. This pigment is initially synthesized in the eggshell gland within the oviduct of laying hens and is subsequently deposited throughout the cuticular and calcareous layers of brown eggshell. In this review, we describe the factors affecting brown eggshell color and potential targets for the regulation of pigment synthesis. Protoporphyrin IX synthesis might be compromised by synthetase-mediated pigment synthesis, the redox status of the female birds, and regulation of the nuclear transcription factors associated with δ-aminolevulinic acid synthetase1. We believe that this review will provide a valuable reference for those engaged in studying eggshell depigmentation.

Effect of genotype and some shell quality traits on lysozyme content and activity in the albumen of eggs from hens under the biodiversity conservation program

The aim of the study was to determine shell quality of eggs laid by some strains of native breed hens of different ages, with special consideration of their effect on lysozyme concentration and enzymatic activity. Evaluation was made of the eggshells from 6 breeds/strains of laying hens covered by the gene pool protection program in Poland: Greenleg Partridge (Z-11), Yellowleg Partridge (Ż-33), Rhode Island Red (R-11), Rhode Island White (A-33), Sussex (S-66), and Leghorn (H-22). Significant (P ≤ 0.01) differences were established for all the shell quality characteristics between hen strains. As the birds aged, shell weight and porosity increased, and shell compression strength decreased in all the experimental groups. Lysozyme content was lowest in white-shelled eggs (H-22) and highest in cream-colored and light brown eggs (Z-11, Ż-33, and R-11). Furthermore, age of hens had a greater effect on lysozyme concentration and activity in the eggs than on shell quality traits. Regardless of the layer genotype, eggs from older hens showed higher lysozyme concentration and enzymatic activity.

Mitochondrial transcription factor A induces the declined mitochondrial biogenesis correlative with depigmentation of brown eggshell in aged laying hens

Eggshell color is an important characteristic for poultry eggs. Eggs from aged hens usually have poor shell color that is unacceptable for the table egg market. The objective of this study was to examine effects of pigment synthesis and mitochondrial biogenesis on brown eggshell color of aged laying hens. In this trial, 8 hens laying eggs with darker shell color and 8 hens laying eggs with lighter shell color were selected from 300 62-week-old Hy-Line brown-egg laying hens. Results showed that egg weight (P < 0.05), eggshell weight (P < 0.01), protoporphyrin IX (Pp IX) content of the eggshell and the shell gland (P < 0.001), and biliverdin content of the shell gland (P < 0.001) were significantly declined in the light-shell group compared with the dark-shell group. Relative mRNA expression of δ-aminolevulinic acid synthase1 (ALAS1) (P < 0.05), coproporphyrinogen oxidase (P < 0.01), ATP-binding cassette transporter ABCG2 (P < 0.01), and mitochondrial transcription factor A (P < 0.05) was reduced in hens laying lighter brown eggshell. Moreover relative mRNA expression of mitochondrial DNA copy number (P < 0.01), mitochondrial NADH dehydrogenase subunit 4 (P < 0.05), mitochondrial ATP synthase F0 subunit 8 (P < 0.05), and mitochondrial cytochrome c oxidase 1 (P < 0.01) was significantly decreased in the shell gland of the light-shell group. In addition, NAD⁺ contents of the shell gland were increased in the dark-shell group (P < 0.01). Brown eggshell depigmentation is a result of decreased Pp IX content in the eggshell and the shell gland. Decreased mitochondrial biogenesis may contribute to the depigmentation of brown eggshell by targeting ALAS1 and ALAS1-mediated Pp IX biosynthesis.

Uterine transcriptome analysis reveals mRNA expression changes associated with the ultrastructure differences of eggshell in young and aged laying hens

Background

Lower eggshell quality in the late laying period leads to economic loss. It is a major threat to the quality and safety of egg products. Age-related variations in ultrastructure were thought to induce this deterioration. Eggshell formation is a highly complex process under precise regulation of genes and biological pathways in uterus of laying hens. Herein, we evaluated the physical, mechanical and ultrastructure properties of eggshell and conducted RNA sequencing to learn the transcriptomic differences in uterus between laying hens in the peak (young hens) and late phase (aged hens) of production.

Results

The declined breaking strength and fracture toughness of eggshell were observed in aged hen group compared to those in young hen group, accompanied with ultrastructure variations including the increased thickness of mammillary layer and the decreased incidence of early fusion. During the initial stage of eggshell formation, a total of 183 differentially expressed genes (DEGs; 125 upregulated and 58 downregulated) were identified in uterus of laying hens in the late phase in relative to those at peak production. The DEGs annotated to Gene Ontology terms related to antigen processing and presentation were downregulated in aged hens compared to young hens. The contents of proinflammatory cytokine IL-1β in uterus were higher in aged hens relative to those in young hens. Besides, the genes of some matrix proteins potentially involved in eggshell mineralization, such as ovalbumin, versican and glypican 3, were also differentially expressed between two groups.

Conclusions

Altered gene expression of matrix proteins along with the compromised immune function in uterus of laying hens in the late phase of production may conduce to age-related impairments of eggshell ultrastructure and mechanical properties. The current study enhances our understanding of the age-related deteriorations in eggshell ultrastructure and provides potential targets for improvement of eggshell quality in the late laying period.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12864-020-07177-7.