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Egg is an encapsulated source of macro and micronutrients that meet all requirements to support embryonic development until hatching. The perfect balance and diversity in its nutrients along with its high digestibility and its affordable price has put the egg in the spotlight as a basic food for humans. However, egg still has to face many years of nutritionist recommendations aiming at restricting egg consumption to limit cardiovascular diseases incidence. Most experimental, clinical, and epidemiologic studies concluded that there was no evidence of a correlation between dietary cholesterol brought by eggs and an increase in plasma total-cholesterol. Egg remains a food product of high nutritional quality for adults including elderly people and children and is extensively consumed worldwide. In parallel, there is compelling evidence that egg also contains many and still-unexplored bioactive compounds, which may be of high interest in preventing/curing diseases. This review will give an overview of (1) the main nutritional characteristics of chicken egg, (2) emerging data related to egg bioactive compounds, and (3) some factors affecting egg composition including a comparison of nutritional value between eggs from various domestic species.

We assessed the effects of supplementation of broiler breeder diets with polyunsaturated fatty acids (PUFA) and organic Se on hatching egg quality during storage. Broiler breeders (n = 352) were fed 1 of 4 diets: SO (soybean oil with no added Se), SO with Se (SO+Se), fish oil (FO), or FO and Se (FO+Se). Eggs from prepeak (23 wk) and peak production (27 wk) breeders were stored for 14 d under typical (15 degrees C, 78% RH) conditions. Eggs were analyzed for albumen Haugh units (HU) and pH, shell characteristics, egg component weight, Se content, and fatty acid (FA) profile. The efficiency of transfer of Se into the egg was greater in low Se treatments compared with in high Se treatments. The majority of Se from the low Se treatments was deposited in the yolk, whereas in high Se treatments, the Se was deposited evenly in the yolk and albumen. In the low Se treatments, the Se content of yolk and albumen was lower than in the high Se treatments and decreased as age increased. Albumen HU decreased with increased storage, although high Se treatments had greater HU compared with low Se treatments. Eggs from the FO treatment were smaller with thinner eggshells compared with the SO treatment, but addition of Se to the FO diets ameliorated some of these effects. The egg yolk FA profile from the SO+Se treatment was altered compared with that from the SO treatment, perhaps due to interactions between dietary PUFA and Se-dependent enzyme systems. Hatching egg quality during storage was affected by dietary PUFA and Se content, as well as broiler breeder age.

Lutein is being considered as a nutrient for prevention of macular degeneration in the aging population. Two experiments were designed to study the transfer efficiency of lutein from the layers' diet into the egg. In experiment 1, laying hens were fed corn-soy diets supplemented with 0, 125, 250, 375, 500, 625, 750, or 1,000 ppm of lutein. After 30 d, eggs were collected and assayed for lutein. In a second study, layers were fed corn-soy diets or diets containing corn gluten meal and alfalfa, with or without added flaxseed. Diets in experiment 2 were supplemented with 0, 125, 250, or 500 ppm of lutein. Adding lutein to the layers' diet resulted in a significant (P < 0.01) increase in Roche color score of yolk within 7 d of plementation. In experiment 1, lutein was transferred into the yolk (P < 0.01) increasing from a basal level of 0.3 mg to 1.5 mg/60 g of egg. However, there was no significant (P > 0.05) increase in yolk lutein with diet supplements >375 ppm. In the second experiment, using corn gluten meal and alfalfa further increased lutein content that leveled off at 2.2 mg/60 g of egg with a diet supplement of 500 ppm of lutein. Adding flax to these diets seemed to depress yolk lutein content. Yolk lutein content can be increased, although further studies are needed to investigate the major decline in transfer efficiency seen with higher levels of dietary supplementation.

Prenatal resource allocation to offspring can be influenced by maternal environment and offspring value, and affect offspring survival. An important pathway for flexible maternal allocation is via egg components such as nutrients and hormones. In cooperative breeders, females with helpers may increase resource allocation to eggs—‘differential allocation’—or reduce it—‘load-lightening’. Yet, helper effects on egg composition have been poorly studied. Moreover, it is unknown how helpers’ presence modulates laying order effects on egg content and survival. Here, we investigated how maternal allocation varied with group size and laying order in the cooperatively breeding sociable weaver (Philetairus socius). We estimated interactive effects of helpers and laying order on allocation to egg mass, yolk nutrients—yolk mass, proteins, lipids, carotenoids, vitamin A and vitamin E—and hormones—testosterone, androstenedione, and corticosterone. Results concurred with the ‘differential allocation’ predictions. Females with more helpers produced later-laid eggs with heavier yolks and more lipids, and laid eggs overall richer in lipids. Proteins, antioxidants, and hormones were not found to vary with helper number. We then analyzed how helper number modulated laying order effects on survival. Females with more helpers did not specifically produce later-laid eggs with higher survival, but eggs laid by females with more helpers were overall more likely to fledge. These findings show that some egg components (yolk mass, lipids) can positively vary according to females’ breeding group size, which may improve offspring fitness.

This study was carried out on 96 caged Bovans Brown laying hens at an initial age of 25 weeks, which were randomly assigned to four experimental groups of 12 replicates (cages) of two hens per cage. The control group hens received a diet containing 20% soybean meal (SBM), without Hermetia illucens larvae meal (HIM) content. The hens in the experimental groups received a diet containing defatted HIM at levels of 5, 10, and 15% (HIM 5%, HIM 10%, and HIM 15%, respectively), at the expense of a proportionally decreasing content of SBM. During the 12-week experiment, the laying performance, biochemical and redox blood indices, and liver condition were examined. The cholesterol level, fatty acid profile, and malondialdehyde content in egg yolks were also evaluated to determine the dietary quality of the eggs. The inclusion of HIM at any level in the diet did not affect the laying performance parameters (p > 0.05). Increased serum Ca and uric acid contents were observed. There was no effect on the redox indices in plasma. The number of hepatocytes was decreased in the HIM-fed groups. The level of cholesterol in yolks was reduced, and the fatty acid profile showed significant changes. Despite the high lauric acid content in the H. illucens meal, it was present in trace amounts in yolks. In the HIM-fed groups, the levels of saturated fatty acids increased significantly, whereas those of unsaturated fatty acids decreased in the yolks in the same groups.

The use of allium extract containing propyl propane thiosulfonate (PTSO) as hen feed supplement was evaluated to demonstrate its positive effect on egg production and intestinal microbiota modulation. The study was carried out on 90 laying hens whose feed was supplemented with allium extract for 28 days. Nutritional properties of eggs were not affected, whereas an improvement in productivity was observed based on the increase weight of eggs. In addition, a modulator effect on intestinal microbiota was confirmed by the increase in Lactobacillus spp. and Bifidobacterium spp., as well as by the reduction in Enterobacteriaceae populations. Finally, the preservation of egg composition was checked by monitoring the content of PTSO, using a new analytical method consisting of the use of solid phase extraction and ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Consequently, based on current results, Allium spp. extract rich in organosulfur compounds such as PTSO added to the diet had a beneficial effect on the microbiota and would seem to be a possible alternative to increase productivity, while not affecting the biochemical composition of egg. However, further studies on the effects of allium extract as feed supplement are necessary.

Eggs of marine organisms are increasingly being recognized as important components of marine food webs. The degree to which egg fatty acid profiles reflect maternal diet fatty acid profiles, and therefore the value of fatty acids in eggs as trophic biomarkers, depends on the species' reproductive strategy and the extent of modification of ingested fatty acids. We measured the dynamics of transfer of recently ingested fatty acids to spawned eggs in a batch-spawning teleost, red drum ( Sciaenops ocellatus ). Results of 21 diet-shift experiments, from which the fatty acid profiles of the diets and eggs were compared, showed that 15 of 27 fatty acids measured (one saturated, two monounsaturated and 12 polyunsaturated fatty acids) in eggs were correlated with their levels in the recent diet, and the rate of incorporation into eggs was proportional to the magnitude of the diet shift. Large shifts in diet might occur naturally during spawning migrations or when prey communities vary over time. Results of this study indicate that fatty acids in red drum eggs can be useful for studying adult diet and exploring trophic linkages in marine systems. This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

The objective of this study was to investigate the effects on laying performance, egg quality traits, color, and composition of supplementing a white corn-based diet with Desmodium tortuosum leaf flour. Three hundred 32-week-old hens were distributed to 30 pens of 10 hens each and allocated to six dietary treatments (five replicates per treatment) for 13 weeks. Two control groups of 50 hens received one of either diet Y, based on yellow corn, or diet W, based on white corn. The other groups received a diet based on white corn supplemented with Desmodium tortuosum leaf flour at 2.5%, 5%, 7.5%, or 10% (diet D). Diet D improved laying performance and yolk color at a reduced feed cost per egg but had no effect on cholesterol content. In conclusion, the inclusion of Desmodium tortuosum leaf flour, in a white corn-based diet, is effective in lowering feed cost, increasing egg production, and improving yolk color.

In this study, the biochemical composition of wild and farm origin grayling eggs was compared, first, to evaluate the composition of fatty acids and protein content in grayling eggs for the first time, and second, to discover differences in biochemical composition between wild and farm origin eggs which is affected by broodstock feed. Farm origin grayling females were fed commercial trout starter feed, while wild origin females were feeding on food present in their natural environment. Fatty acid composition, protein content and colour were determined. Based on a principle component analysis (PCA) of the biochemical profile, farm and wild origin grayling eggs were clearly separated. Wild origin grayling eggs contained higher amount of SFA, but lower MUFA and PUFA than farm origin eggs. A considerable difference between wild and farm origin grayling eggs was observed also in essential fatty acids: C22:6 n-3 (DHA), C20:5 n-3 (EPA) and C20:4 n-6 (ARA), resulting in higher EPA/ARA and DHA/EPA ratio in farm origin eggs compared to wild origin eggs. Wild origin grayling eggs were characterised by higher protein content and were more intensely red-coloured than farm origin eggs, which were almost colourless. It could be concluded that the biochemical composition of farm origin eggs significantly differs from wild origin grayling eggs, which might have an influence on the embryonic development and hatching success of farm origin grayling. Therefore, the diet that has the greatest effect on egg composition needs to be optimised to meet the needs of the grayling broodstock and to improve the breeding efficiency of farm raised graylings.

Female birds can influence offspring development by adjusting egg size or by a differential allocation of egg resources. Such maternal effects can be expected to be shaped by natural selection, given the costs connected to the allocation of maternal resources. Among egg components, yolk androgens play an important role in affecting offspring life-history traits. Despite their relevance for nestling development, factors accounting for the observed within- and between-clutch variation are still poorly known. By using a cross-sectional sampling approach, we tested the effect of female age, laying order and laying date on the deposition of yolk androstenedione (A4) and testosterone (T), since young and older females could maximize their fitness differently according to breeding conditions. We found a remarkable lack of differences in overall yolk androgen levels across different ages. However, comparing first-year with older females, our results showed that age did not influence yolk T levels at the beginning of the breeding season, whereas at the end, first-year females transferred lower hormone levels than older females. Within clutches, both androgens increased across the laying sequence, suggesting that late nestlings benefit from an increased allocation that could compensate hatching asynchrony. However, when considering A4, we found that, whereas older females always increased A4 levels across the laying sequence, first-year females did not increase it at the end of the breeding season, thus increasing the likelihood of brood reduction when environmental conditions became hardest. These findings suggest that yolk A4 variation may be particularly important at the within-clutch scale, by providing females with a tool to modify nestling hierarchies.