Search

Fresh duck eggs normally have an unpleasant fishy odor when compared with eggs from other poultry. However, the cause of this unpleasant smell remains unknown. Besides, we have limited knowledge regarding the perception ability of this odor. Therefore, we aimed to identify the causative substances responsible for the fishy odor in duck eggs, and further evaluate the factors affecting the perception ability of this odor. We detected and quantified the volatile substances in the yolks of Jingjiang duck and Beijing duck eggs using headspace gas chromatography, and evaluated the fishy odor rating scores. We performed association studies on the relationship between the relative content of volatile substances and fishy odor rating scores. The fishy odor of egg yolks from different species/breeds was also characterized. Furthermore, we assessed the species/breeds of poultry eggs and the effects of gender and region of the evaluators on the fishy odor rating score by using an ordinal logistic regression model. Results showed that trimethylamine (TMA) is responsible for the fishy odor of duck eggs, which was confirmed with subsequent verification (P < 0.001). The fishy odor of duck eggs was stronger than that of chicken eggs; the fishy odor of Jingjiang duck eggs was the strongest. Results also indicated that the fishy odor perception ability was affected by the gender and region of the evaluators (P < 0.001). Overall, these data clarified that TMA imparted the fishy odor to duck eggs; factors such as gender and region may affect the fishy odor perception ability., (© 2019 Poultry Science Association Inc.)

Background: Eggshell is subject to quality loss with aging process of laying hens, and damaged eggshells result in economic losses of eggs. However, the genetic architecture underlying the dynamic eggshell quality remains elusive. Here, we measured eggshell quality traits, including eggshell weight (ESW), eggshell thickness (EST) and eggshell strength (ESS) at 11 time points from onset of laying to 72 weeks of age and conducted comprehensive genome-wide association studies (GWAS) in 1534 F2 hens derived from reciprocal crosses between White Leghorn (WL) and Dongxiang chickens (DX)., Results: ESWs at all ages exhibited moderate SNP-based heritability estimates (0.30 ~ 0.46), while the estimates for EST (0.21 ~ 0.31) and ESS (0.20 ~ 0.27) were relatively low. Eleven independent univariate genome-wide screens for each trait totally identified 1059, 1026 and 1356 significant associations with ESW, EST and ESS, respectively. Most significant loci were in a region spanning from 57.3 to 71.4 Mb of chromosome 1 (GGA1), which together account for 8.4 ~ 16.5% of the phenotypic variance for ESW from 32 to 72 weeks of age, 4.1 ~ 6.9% and 2.95 ~ 16.1% for EST and ESS from 40 to 72 weeks of age. According to linkage disequilibrium (LD) and conditional analysis, the significant SNPs in this region were in extremely strong linkage disequilibrium status. Ultimately, two missense SNPs in GGA1 and one in GGA4 were considered as promising loci on three independent genes including ITPR2, PIK3C2G, and NCAPG. The homozygotes of advantageously effective alleles on PIK3C2G and ITPR2 possessed the best eggshell quality and could partly counteract the negative effect of aging process. NCAPG had certain effect on eggshell quality for young hens., Conclusions: Identification of the promising region as well as potential candidate genes will greatly advance our understanding of the genetic basis underlying dynamic eggshell quality and has the practical significance in breeding program for the improvement of eggshell quality, especially at the later part of laying cycle.

Beijing-you is a Chinese local chicken which is raised for both meat and eggs. In the present study, we detected the effects of different rearing systems on growth, slaughtering performances and meat quality of Beijing-you chickens at 26-40 weeks of age. Six hundred Beijing-you hens were randomly allocated into two groups at 16 weeks of age and raised in free range or battery cage systems. The body weight, slaughtering performance and meat quality were measured for each group at the ages of 26, 30, 35 and 40 weeks. Some of the traits were dramatically influenced by the two systems, although most of them did not show significant changes. For the meat fiber microstructure, we found that the diameter of thigh and breast muscle fiber in the free range group were significantly increased than in the cage group (P < 0.05) at 26 weeks of age. The ratio of fast muscle fiber in thigh muscle samples of the free range group was significantly reduced compared to that of cage group at both 35 (P < 0.01) and 40 (P < 0.01) weeks of age, indicating that the free range system could promote the transforming of fast muscle fiber to slow muscle fiber., (© 2014 Japanese Society of Animal Science.)

One of the main concerns for poultry producers is how to maintain egg uniformity and stability in size and weight following the rapid growth during the early laying period. In this study, we aimed to investigate the increase in egg weight with advancing hen age, and to estimate genetic parameters of these increment traits in 2 pure lines of chickens (i.e., 2,010 White Leghorn and 1,200 brown-egg dwarf hens), using the restricted maximum likelihood method with the DMU procedure. We collected age at first egg (AFE), first egg weight (FEW) and kept records of egg weight per 10 wk from 30 to 60 wk of age. Meanwhile, the increments of egg weight were calculated for the evaluation of age-dependent dynamic changes. The increment of egg weight gained dramatically before 30 wk of age and became slower with the advance of age. Heritability estimates of AFE were larger than 0.32, and the low to moderate genetic correlations between AFE and FEW were observed in the 2 lines. The FEW showed high variation level compared with egg weights at later ages in the 2 lines, and had moderate heritability estimates in White Leghorns (0.20) and dwarf hens (0.33). Egg weights at different ages were highly heritable in the 2 lines (h(2) ≥ 0.35), and had strong genetic and phenotypic correlations among different ages. The estimates of heritability for most increment traits were low to moderate, especially those increments for 10-wk intervals ranging from 0.00 to 0.14. The genetic correlations among 3 consecutive egg weight increments for 10-wk intervals were low to moderate. Our results in the 2 lines should provide important insights into the genetic architecture of increment traits and offer some suggestions for producing uniform and stable eggs in response to advancing age., (©2014 Poultry Science Association Inc.)

Eggshell strength is a crucial economic trait for table egg production. During the process of eggshell formation, uncalcified eggs are bathed in uterine fluid that plays regulatory roles in eggshell calcification. In this study, a label-free MS-based protein quantification technology was used to detect differences in protein abundance between eggshell matrix from strong and weak eggs (shell matrix protein from strong eggshells and shell matrix protein from weak eggshells) and between the corresponding uterine fluids bathing strong and weak eggs (uterine fluid bathing strong eggs and uterine fluid bathing weak eggs) in a chicken population. Here, we reported the first global proteomic analysis of uterine fluid. A total of 577 and 466 proteins were identified in uterine fluid and eggshell matrix, respectively. Of 447 identified proteins in uterine fluid bathing strong eggs, up to 357 (80%) proteins were in common with proteins in uterine fluid bathing weak eggs. Similarly, up to 83% (328/396) of the proteins in shell matrix protein from strong eggshells were in common with the proteins in shell matrix protein from weak eggshells. The large amount of common proteins indicated that the difference in protein abundance should play essential roles in influencing eggshell strength. Ultimately, 15 proteins mainly relating to eggshell matrix specific proteins, calcium binding and transportation, protein folding and sorting, bone development or diseases, and thyroid hormone activity were considered to have closer association with the formation of strong eggshell., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Quail eggs comprise a significant and favourable part of table eggs in certain countries. Some quail eggs, however, present fishy off-flavor which directly influences their quality. It is reported that flavin-containing monooxygenase 3 (FMO3) is associated with fish-odour trait in human and animal products. FMO3 is responsible for the degradation of trimethylamine (TMA) in vivo. Loss-of-function mutations in FMO3 gene can result in defective TMA N-oxygenation, giving rise to disorder known as "fish-odour syndrome" in human, as well as the fishy off-flavor in cow milk and chicken eggs. In order to reveal the genetic factor of fishy taint in quail eggs, we cloned the cDNA sequence of quail FMO3 gene, investigated FMO3 mRNA expression level in various tissues, detected SNPs in the coding region of the gene and conducted association analysis between a mutation and the TMA content in quail egg yolks. The 1888 bp cDNA sequence of quail FMO3 gene encoding 532 amino acids was obtained and characterized. The phylogenetic analysis revealed quail FMO3 had a closer relationship with chicken FMO3. The FMO3 mRNA was highly expressed in liver and kidney of quail. Nine SNPs were detected in the coding sequence of quail FMO3 gene, including a nonsense mutation (Q319X) which was significantly associated with the elevated TMA content in quail egg yolks. Genotype TT at Q319X mutation loci was sensitive to choline. With addition of choline in the feed, the quails with homozygote TT at the Q319X mutation loci laid fish-odour eggs, indicating an interaction between genotype and diet. The results indicated that Q319X mutation was associated with the fishy off-flavor in quail eggs. Identification of the unfavorable allele T of quail FMO3 gene can be applied in future quail breeding to eliminate fishy off-flavor trait in quail eggs.

Lipids are commonly incorporated into the diets of laying hens at a rate of 1% to 2% during production. However, the effects on egg quality can vary based on the source and timing of lipid addition. Hence, this experiment was conducted to investigate the impacts of adding the same concentration of soybean oil, lard, and mixed oils (1.5%) to the daily feed of layer during two feeding periods. This study aimed to assess the changes in nutritional composition and functional properties and offer valuable insights to determine suitable types of oils and fat. In this study, the experiment was conducted in two test periods, 7 days and 21 days after the addition of the lipids, to assess the effects on the nutritional composition and functional properties of eggs. The study revealed the following results: (1) Changes in the yolk's nutritional composition. Compared to the 7-day addition period, the inclusion of lard significantly increased the unsaturated fatty acids after 21 days; (2) Changes in the albumen's nutritional composition. Compared to the 7-day addition period, the inclusion of lard and mixed oils significantly reduced the essential and nonessential amino acids after 21 days; (3) Changes in the functional characteristics of the eggs. After 21 days of addition, the eggs from the soybean oil group exhibited significantly higher foaming and emulsifying properties compared to the groups supplemented with lard and mixed oils; (4) Changes in the antioxidant capacity of the eggs. Compared to the 7-day addition period, the inclusion of all oils and fat significantly increased the superoxide dismutase (SOD) content in egg yolk after 21 days. The aim of this experiment was to provide valuable scientific data to assist producers in making informed decisions regarding the utilization of feeding oils. [ABSTRACT FROM AUTHOR]

Egg quality and nutritional value are becoming increasingly important to consumers, offering a new direction for the development of high-quality eggs. In this study, we conducted a comprehensive analysis of egg quality and nutrient profiles in native breeds at different ages, integrating pedigree data. Our results reveal dynamic changes in egg qualities, stronger associations among eggshell-related traits, and the effect of onset production and body weight on egg qualities. The heritability of different traits was estimated, ranging from 0.05 to 0.62. Subsequently, we elucidated that the moisture and nutritional content in the egg yolk were not influenced by the percentage of yolk but were indeed subject to age regulation. There was a notable decrease in moisture, an elevation in crude fat, and an increase in the diversity of fatty acids of yolk with advancing age. In summary, investigating the trends and interrelationships in egg quality, nutrient content, and heritability across the whole laying cycle offers valuable insights for breeders to optimize feeding management strategies and aids consumers in meeting their expectations of egg quality. [ABSTRACT FROM AUTHOR]

Simple Summary: n-3 PUFA, selenium and lutein cannot be synthesized in the human body, but these substances are very important for human health. Consuming functional eggs enriched with nutrients can increase the body's intake of these substances. To efficiently produce functional eggs, selecting breeds that can deposit higher levels of these nutrients is necessary. Therefore, we investigated the types, dosages, and cycles of additives used in the production of functional eggs. In Trial 1, we investigated the differences in n-3 PUFA deposition among five breeds of eggs. The results showed significant variations in the ability of different breeds to deposit n-3 PUFA in eggs, with Dwarf Layer demonstrating a significant advantage. In Trial 2, we investigated the difference of n-3 PUFA, selenium and lutein deposition in eggs from two reeds in terms of their ability to deposit selenium and lutein in eggs. Additionally, the n-3 PUFA content in eggs from the two breeds was similar to the findings in Trial 1. Therefore, this experiment provides valuable insights for selecting different breeds in the production of functional eggs, ultimately improving the quality and economic benefits of the production process. The purpose of this study was to compare the differences in the content of functional nutrients in eggs, performance parameters, and egg quality parameters of different chicken breeds. In Trial 1, 150 41-week-old hens of each breed, including the Dwarf Layer, White Leghorn, Silky fowl, Beijing-you chicken, and Shouguang chicken, were randomly assigned to the control (CON) and 2.5% flaxseed oil (FSO) groups to compare the difference in n-3 polyunsaturated fatty acid (PUFA) content in eggs. The contents of α-linolenic acid (ALA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and total n-3 PUFA in eggs were increased (p < 0.05) in the FSO groups. The ALA (4.28%), DHA (2.03%), and total n-3 PUFA (6.46%) contents in eggs of Dwarf Layer were the highest among the five breeds (p < 0.05). To further verify if other functional nutrients also have such differences, 600 24-week-old White Leghorn and Dwarf Layer were allocated to four groups: CON, FSO, 0.02% selenium-enriched yeast (SEY), and 0.20% marigold flower extract (MFE), in Trial 2. The content of functional nutrients in eggs was significantly increased (p < 0.05) after feeding these additions. After feeding FSO, the eggs of the Dwarf Layer had a higher n-3 PUFA content than the White Leghorn (p < 0.05). However, no significant differences were found in selenium and lutein content in different breeds. Performance and egg quality were not negatively impacted by FSO, SEY, or MFE. [ABSTRACT FROM AUTHOR]

Translucent egg consumption is low due to consumer acceptance and quality concerns, which is a problem that egg producers need to address. This study was performed to evaluate the reasons for the high occurrence of egg translucency in summer, as well as whether the addition of mono-dicalcium phosphate (MDCP) to the diet can relieve eggshell translucency and whether eggshell translucency is associated with the risk of bacterial invasion. A total of 72 laying hens that were 36 weeks old were randomly divided into control (CON) and MDCP groups and fed in the same environment. Results showed that the number of translucent eggs increases in July and August as the temperature and humidity increase. Compared with the CON group, in July, August, and October, the translucent egg grade (TEG) of the MDCP group was lower than that of the CON group (p < 0.05). TEG was correlated with mastoid space height (MSH), width (MSW), and area (MSA) (correlation coefficients 0.63, 0.59, and 0.68, respectively, p ≤ 0.05). There was no significant difference in the invasion rate of E. coli between translucent and non-translucent egg groups (47.2% vs. 39.33%), and translucent area and non-translucent area (13.49% vs. 15.08%). In conclusion, our results show that dietary MDCP may alleviate eggshell translucency and that eggshell translucency would not increase the probability of E. coli cross-shell penetration rate. [ABSTRACT FROM AUTHOR]

The cuticle formed in the uterus is the outermost layer as the first defense line of eggshell against microbial invasions in most avian species, and analyzing its genetic regulation and influencing factors are of great importance to egg biosecurity in poultry production worldwide. The current study compared the uterine transcriptome and proteome of laying hens producing eggs with good and poor cuticle quality (GC and PC, the top and tail of the cuticle quality distribution), and identified several genes involved with eggshell cuticle quality (ESCQ). Overall, transcriptomic analysis identified 53 differentially expressed genes (DEGs) between PC versus GC group hens, among which 25 were up-regulated and 28 were down-regulated. No differences were found in the uterine proteome. Several DEGs, including PTGDS, PLCG2, ADM and PRLR related to uterine functions and reproductive hormones, were validated by qPCR analysis. Egg quality measurements between GC and PC hens showed GC hens had longer laying interval between two consecutive ovipositions (25.64 ± 1.23 vs 24.94 ± 1.12 h) and thicker eggshell thickness (352.01 ± 23.04 vs 316.20 ± 30.58 μm) (P < 0.05). Apart from eggshell traits, other egg quality traits didn't differ. The result demonstrated eggshell and cuticle deposition duration in the uterus is one of the major factors affecting ESCQ in laying hens. PTGDS, PLCG2, ADM and PRLR genes were discovered and might play crucial roles in cuticle deposition by regulating the uterine muscular activities and secretion function. The findings in the present study provide new insights into the genetic regulation of cuticle deposition in laying hens and establish a foundation for further investigations. [ABSTRACT FROM AUTHOR]

Eggshell color is the most intuitive external feature that affects consumer acceptance. Different eggshell colors are mainly determined by protoporphyrin IX and biliverdin content. The selection of eggshell color by the human eye with an eggshell color fan can be roughly classified. Although more technologically advanced, a colorimeter or spectrophotometer might be of limited use when observing a variety of shell colors, such as brown, olive, green, and blue. This study aimed to provide a convenient and accurate method for predicting the content of eggshell pigments by measuring eggshell color using the Commission International de L'Eclairage (CIE) L*a*b* system. The results showed the deepening of eggshell color in brown and blue eggs was correlated with increased eggshell pigment deposition, and eggshell color was significantly positively correlated with eggshell pigment content (P < 0.01). Furthermore, the adjusted R2 of the fitted function was in the range of 0.81 to 0.89, and the Spearman rank correlation coefficient between the predicted and true values was in the range of 0.89 to 0.93. In brief, the L*a*b* method of measuring eggshell color to predict the amount of eggshell pigment deposition is convenient, effective, and promising for layer production. [ABSTRACT FROM AUTHOR]

Studies on trimethylamine (TMA) in egg yolk have focused on how it impacts the flavor of eggs, but there has been little focus on its other functions. We designed an in vitro antibacterial test of TMA according to TMA concentrations that covered the TMA contents typically found in egg yolk. The change in TMA content in yolk was analyzed at different storage temperatures and for different storage durations. The known antibacterial components of eggs, including the cuticle quality of the eggshell and the lysozyme activity and content in egg white, were also assessed. The total bacterial count (TBC) of different parts of eggs were detected. The results showed that the inhibitory effect of TMA on Escherichia coli (E. coli) growth increased with increasing TMA concentration, and the yolk TMA content significantly increased with storage duration (p < 0.05). The cuticle quality and lysozyme content and activity significantly decreased with storage time and increasing temperature, accompanied by a significant increase in the TBC on the eggshell surface and in the egg white (p < 0.05). This work reveals a new role for trace TMA in yolks because it reduces the risk of bacterial colonization, especially when the antibacterial function of eggs is gradually weakened during storage. [ABSTRACT FROM AUTHOR]

The nanostructure greatly contributes to eggshell formation, the mechanical properties of eggshells, and mineral dissolution during incubation. In this study, to investigate the effect of the nanostructure on the gloss of eggs, the gloss and eggshell quality (cuticle coverage, color, and thickness) of 105 eggs were measured. According to the order of the gloss, the surface roughness of 30 high-gloss and 30 low-gloss eggs was compared. The gloss had no significant correlation with the eggshell color and thickness (P > 0.05) and a significant relationship with the cuticle coverage (r = 0.19, P < 0.01). The surface roughness significantly differed between the high- and low-gloss eggs (P < 0.001), and the gloss was negatively correlated with the surface roughness (r (high-group) = −0.61, r (low-group) = −0.56, P < 0.01). The shell gloss of 30 oiled eggs with mineral oil and 30 normal eggs from commercial brown-egg layers was also compared. The oil coating increased the eggshell gloss, but the roughness was unchanged. This is the first report to establish the contribution of nanostructure for the gloss of chicken eggshell. The surface roughness can be used as an indicator of the gloss, which could be helpful for selective breeding to improve the eggshell brightness. Our research also provides the foundation for further investigation of the effect of non-pigmentary contributors on the chicken eggshell appearance. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the characteristics of egg consumption in China and the production of functional eggs, and finally enrich the types of shell egg products. Trial 1 explored the influence of egg quality on Chinese consumers' willingness to purchase eggs through a questionnaire, which investigated 1,317 consumers' preferences for egg appearance, factors influencing egg purchase, and purchase of functional eggs. The results showed that about 65% of respondents ate more than 4 eggs per wk, pink eggs were the most popular in China, about 65% of consumers preferred eggs with an egg weight of 48 to 58 grams. For functional eggs, 75.32% of consumers have never heard of them. Preferences for eggshell color and yolk color varied by geographic region, with darker colors preferred in Northeast China. Based on the survey results of functional eggs consumption in Trial 1, the dwarf layers of China Agricultural University were used in Trial 2 to produce functional eggs. The eggs are small and pink in color, which is in line with the preferences of Chinese consumers. Three hundred dwarf layers were divided into 4 groups, using the linseed oil added, marigold extract added, and yeast selenium added diets to produce normal, n-3 fatty acid-enriched, lutein-enriched and selenium-enriched eggs by feeding for 28 d, determined the eggs' nutrient content and egg quality. The results showed that the n-3 fatty acid, lutein and selenium contents of the eggs of dwarf layers were significantly increased by changing the diets and did not affect the egg weight, eggshell strength, Haugh units or the proportion of egg parts. The results of this study are helpful to understand the trend of egg consumption preferences in China, and on this basis to produce functional eggs that meet the consumers' expectations. [ABSTRACT FROM AUTHOR]

Current analytical methods used for composition analysis of egg products are time consuming and laborious. We developed a near-infrared reflectance spectroscopy (NIRS)-based method to determine the fat, moisture, and protein contents in homogenized egg yolk and the moisture and protein contents in homogenized egg albumen to substitute for conventional methods. The coefficients of determination in the external validation set (R2P) were over 0.8 for all chemical compositions. The ratios of performance to standard deviation (RPD) were 4.38, 2.25, 2.28, 2.31, and 3.03 for fat, moisture, protein and moisture in the egg yolk, and protein in the egg albumen, respectively. Thus, NIR spectroscopy could be an efficient tool for quantitative analysis of the nutrients in chicken eggs. [ABSTRACT FROM AUTHOR]

The fishy odor of duck eggs has restricted their consumption and industrial development, a problem that producers need to address. We estimated the effects of cage, floor, and pond rearing systems on duck egg flavor, egg quality, and microbial diversity by evaluating yolk trimethylamine (TMA) content, egg quality, and the differences between duck cecum (cage cecum, CC ; floor cecum, FC ; pond cecum, PC) and the environment (cage environment, CE ; floor environment, FE ; pond environment, PE). The results show that the yolk TMA content of the floor-rearing and pond-rearing systems was significantly higher than that of the cage-rearing system (P < 0.001), with no difference between the floor and pond-rearing systems. No significant differences were detected in egg quality among the rearing systems. Firmicutes, Actinobacteria, and Bacteroidetes were the dominant phyla in the cecum, and in the rearing environment, Firmicutes, Actinobacteria, Bacteroidetes, and Proteobacteria were the dominant phyla. The results of α and β diversity analyses show that changes in the rearing system affected the composition and diversity of duck cecal microbes. In addition, we screened several genera that may be related to the production of TMA in duck cecum under different rearing systems using LEfSe analysis; for example, Subdoligranulum in the CC group; Romboutsia in the FC group; and Lactobacillus, Clostridium , and Streptococcus in the PC group. In conclusion, the rearing system affects the cecal microbes of ducks, which in turn affect the deposition of TMA in duck eggs but have no adverse effect on egg quality. This study provides a basis for the development of rearing strategies to reduce the fishy odor of egg yolk in the duck industry. [ABSTRACT FROM AUTHOR]

Eggs with the same total weight may have considerable differences in yolk weight. Eggs with a high percentage of yolk have a higher nutritional value, more flavor, and are more desirable to consumers. However, a large yolk proportion means more dry matter in the eggs, which reduces the feed efficiency. The elucidation of the genetic factors of yolk quantity in eggs is of scientific and practical significance. Through RNA sequencing, we explored the transcriptome of ovarian tissue from 12 Wenchang chickens, including 6 chickens that laid eggs with a high yolk percentage (32%) and 6 that laid low yolk percentage eggs (25%). We identified a total of 362 differentially expressed genes (P -value < 0.01, log 2 fold change < −1, log 2 fold change > 1), of which 220 were upregulated and 142 were downregulated in high yolk percentage hens. According to the Gene Ontology terms annotation and Kyoto Encyclopedia of Genes and Genomes enrichment analysis, the differentially expressed genes were associated with the regulation of various cell functions, cell differentiation and development, neuroactive ligand–receptor interactions, and calcium and ubiquitin-mediated proteolysis signaling pathways. To further filter for genes that were directly involved in yolk accumulation, the chicken quantitative trait loci database, genes within 100 kb upstream and downstream of the yolk weight trait SNP, and intersection genes in protein–protein interaction network diagrams were used to detect genes that overlapped with the differentially expressed genes. We found 7 candidate genes in total, MNR2, AOX1, ANTXRL, GRAMD1C, EEF2, COMP , and JUND , which affect female reproductive performance and the growth and development of follicles, supporting cell transport, cell proliferation, and differentiation. All candidate genes and several randomly selected genes were verified by quantitative real time PCR, and the results were consistent with the RNA sequencing. In conclusion, investigating the molecular mechanisms of high yolk percentage traits will allow breeding strategies to be optimized to alter the percentage of yolk in chicken eggs. [ABSTRACT FROM AUTHOR]