QTL mapping of egg albumen quality in egg layers

Background

A fresh, good quality egg has a firm and gelatinous albumen that anchors the yolk and restricts growth of microbiological pathogens. As the egg ages, the gel-like structure collapses, resulting in thin and runny albumen. Occasionally thin albumen is found in a fresh egg, giving the impression of a low quality product. A mapping population consisting of 1599 F₂ hens from a cross between White Rock and Rhode Island Red lines was set up, to identify loci controlling albumen quality. The phenotype for albumen quality was evaluated by albumen height and in Haugh units (HU) measured on three consecutive eggs from each F₂ hen at the age of 40 weeks. For the fine-mapping analysis, albumen height and HU were used simultaneously to eliminate contribution of the egg size to the phenotype.

Results

Linkage analysis in a small population of seven half-sib families (668 F₂) with 162 microsatellite markers spread across 27 chromosomes revealed two genome-wide significant regions with additive effects for HU on chromosomes 7 and Z. In addition, two putative genome-wide quantitative trait loci (QTL) regions were identified on chromosomes 4 and 26. The QTL effects ranged from 2 to 4% of the phenotypic variance. The genome-wide significant QTL regions on chromosomes 7 and Z were selected for fine-mapping in the full set composed of 16 half-sib families. In addition, their existence was confirmed by an association analysis in an independent commercial Hy-Line pure line.

Conclusions

We identified four chicken genomic regions that affect albumen quality. Our results also suggest that genes that affect albumen quality act both directly and indirectly through several different mechanisms. For instance, the QTL regions on both fine-mapped chromosomes 7 and Z overlapped with a previously reported QTL for eggshell quality, indicating that eggshell membranes may play a role in albumen quality.     

31P-NMR characterization of hen egg yolk and egg white

The avian egg is an isolated system where embryonic development can easily be studied. Furthermore, the system can be subjected to various environmental constraints. Its size is such that it can easily be accommodated in most NMR instruments. This is demonstrated by a recent 31P-NMR surface coil experiment where the increase of embryo size and development could be judged by the levels of ATP and phosphocreatine (Belton, P.S., Gordon, R.E., Jones, J.M. and Shaw, D. (1983) Br. Poult. Sci. 24, 429-433).     

Effect of egg storage duration and egg turning during storage on egg quality and hatching of broiler hatching eggs

In commercial hatcheries, it is common to store eggs before incubation. One practice to improve hatchability consists in egg turning during this storage. This work aims to highlight the effects of turning on the physicochemical aspects of eggs and, consequently, how this turning can influence the hatching of chicks. An experiment was conducted to evaluate the effects of storage duration and egg turning during storage on egg quality, hatchability, and residual analysis. A total of 7 500 hatching eggs were collected from a 55-week-old commercial Cobb500 breeder flock and storage according to the treatments. The experiment was completely randomized in a 3 × 2 factorial design with three storage periods (4, 8, and 12 days) and egg turning (180° turn of eggs once a day) or no turning during storage, totaling six treatments. Regardless of turning, eggs stored for 4 days weighed more than turned eggs stored for 8 and 12 days, which were similar (P < 0.05). Non-turned eggs experienced an increase in relative shell weight with increased storage duration, and non-turned eggs stored for 4 and 8 days differed from non-turned eggs stored for 12 days (P < 0.05). Albumen pH of turned eggs stored for 4 and 8 days was lower than that of non-turned eggs stored for the same durations (P < 0.05). Albumen pH of turned eggs increased as storage duration increased (P < 0.05). Egg turning increased hatching by 2.02% over that of non-turning (P < 0.05). Eggs stored for 12 days, irrespective of turning, had higher late embryonic mortality (P < 0.05) compared to the other treatments. It was concluded that turning eggs during pre-incubation storage was adequate to improve hatchability of fertile eggs. Storing fertile eggs for 12 days is harmful to egg quality and increases embryo mortality even if eggs were turned.     

The use of egg chorion glycoprotein of Epinephelus malabaricus for egg identification

An immuno‐probe against a glycoprotein in the egg chorion was developed for egg identification. The 97 kD glycoprotein in the chorion of unfertilized eggs of Epinephelus malabaricus was isolated and separated by SDS‐PAGE as an antigen to induce antibody from rabbit. The reactivity of the antibody as the immuno‐probe to E. malabaricus eggs was significantly positive, and was specific in that it did not react with the eggs of other fish species. The immuno‐probe should be useful in identifying the eggs of E. malabaricus among mixed egg populations.     

Trade-off between egg mass and egg number in brown trout

Individual egg mass and fecundity increased with somatic mass in first time and repeat spawning wild anadromous and freshwater resident brown trout Salmo trutta . The egg mass was larger for similar-sized trout in south (58° N) than mid Norway (63° N), whereas fecundity was higher in mid- than in south Norway, making total gonadal investment similar in the two areas. Repeat spawners had heavier eggs than similar-sized first time spawners. The egg mass of residents was c. 10% larger than that of similar-sized first time spawning anadromous trout. Common garden experiments with offspring of wild anadromous trout showed no significant correlation between egg and somatic mass in first time spawners in two of the three populations studied. In the third population, a slight positive correlation was found. Similar results were found for repeat spawners. In the three populations, fecundity increased significantly with somatic mass in both first time and repeat spawners. Wild and hatchery-reared trout showed negative correlation between egg mass and fecundity when the effect of body size was excluded, indicating a trade-off between the two parameters. In wild trout, this was caused by variation among populations, whereas in hatchery fish, within population variation was observed in egg mass over fecundity. Furthermore, the egg mass of first time and repeat spawners were positively correlated, when adjusted for fish size. Size-specific gonadal investment was significantly higher in wild anadromous than resident trout. There was no significant difference in gonadal investment between first time and repeat spawners in wild anadromous trout. However, in the hatchery-reared trout, gonadal investment was significantly higher at repeat than first time maturation. The hatchery trout did not spawn naturally, but were artificially stripped. Among populations, a part of the variation in egg mass and fecundity is phenotypically plastic, a part appears genetically determined.     

Preventive effect of egg yolk phosvitin on heat-insolubilization of egg white protein and its application to heat-induced egg white gel

The effects of phosvitin (PV) on insolubilization of egg white protein (EWP) and ovotransferrin (OT) were examined by measuring turbidity after heating at 80 degrees C in a pH range of 5 to 8. PV showed preventive ability against heat-insolubilization of EWP, especially heat-labile OT. The preventive ability of PV was reduced by adding NaCl to a PV-OT mixture on heating. Native PAGE and gel filtration analyses showed that PV prevented an insolubilization of heat-denatured OT through ionic interactions. The preventive effects of PV on insolubilization of EWP and OT resulted in the formation of a firm, transparent gel from EWP in coexistence with PV on heating. The addition of PV might make possible the preparation of liquid egg white without insoluble products even on heat-treatment at high temperatures.     

Co-extraction of egg white proteins using ion-exchange chromatography from ovomucin-removed egg whites

Efficient isolation of egg white components is desired due to its potential uses. Existing methods mainly targeted on one specific protein; an attempt has been made in the study to co-extract all the valuable egg white components in a continuous process. Ovomucin was first isolated by our newly developed two-step method; the resultant supernatant obtained after ovomucin isolation was used as the starting material for ion-exchange chromatography. Anion-exchange chromatography of 100 mM supernatant yielded a flow-through fraction and three other fractions representing ovotransferrin, ovalbumin and flavoproteins. The flow-through fraction was further separated into ovoinhibitor, lysozyme, ovotransferrin and an unidentified fraction which represents 4% of total egg white proteins. Chromatographic separation of 500 mM supernatant resulted in fractions representing lysozyme, ovotransferrin and ovalbumin. This co-extraction protocol represents a global recovery of 71.0% proteins.     

Crustacean egg size as an indicator of egg fat/protein reserves

The metabolic properties of crustacean eggs and the major organic reserve utilized for embryogenesis are dependent on the egg-size correlated deposition of fat/protein in the yolk.     

Do polyandrous shorebirds trade off egg size with egg number?

Classical polyandry in birds is rare and is most frequent in the shorebirds (Charadriiformes). Polyandrous shorebirds lay smaller eggs for their body masses than non-polyandrous shorebirds, indicating that polyandrous female shorebirds may trade egg size off against number of eggs in order to maximize reproductive success. However, this trade-off may be confounded by phylogeny because most polyandrous species belong to a single family, the Jacanidae. I re-analysed this adaptive hypothesis using phylogenetically-independent contrast analyses. These analyses showed that there was no statistically significant difference in egg size between polyandrous and monogamous shorebirds once the effects of phylogeny had been incorporated. This is one of the first studies to show that the results of independent contrasts analyses differ from those where phylogenetic effects have not been taken into account.     

Fast egg collection method greatly improves randomness of egg sampling in Drosophila melanogaster

When obtaining samples for population genetic studies, it is essential that the sampling is random. For Drosophila, one of the crucial steps in sampling experimental flies is the collection of eggs. Here an egg collection method is presented, which randomizes the eggs in a water column and diminishes environmental variance. This method was compared with a traditional egg collection method where eggs are collected directly from the medium. Within each method the observed and expected standard deviations of egg-to-adult viability were compared, whereby the difference in the randomness of the samples between the two methods was assessed. The method presented here was superior to the traditional method. Only 14% of the samples had a standard deviation higher than expected, as compared with 58% in the traditional method. To reduce bias in the estimation of the variance and the mean of a trait and to obtain a representative collection of genotypes, the method presented here is strongly recommended when collecting eggs from Drosophila.     

The role of oligosaccharide in transport of egg yolk riboflavin-binding protein to the egg

The carbohydrate portion of chicken egg yolk riboflavin-binding protein was examined to determine its role in the biological activity of the protein. Yolk RBP was found to contain 5–6 mannose, five galactose, 12 N-acetylglucosamine and four sialic acid residues. Specific modifications of the oligosaccharide moiety were performed which included removal of sialic acid by mild acid hydrolysis, oxidation of galactose oxidase, and removal of N-acetylglucosamine and galactose residues by a mixture of glycosidases from Aspergillus niger. All of the modified proteins retained the ability to bind riboflavin although their capacities were lower than that of native yolk RBP. Circular dichroism of the modified yolk RBP samples showed changes in the near ultraviolet, but molar ellipticities in the far ultraviolet displayed only minor variations indicating no gross structural changes. All samples cross-reacted with RBP-specific antiserum. The plasma half-life of ¹²⁵I-labeled yolk RBP was 62 min. Each of the modified samples was cleared more rapidly from the blood than native yolk RBP. Removal of sialic acid decreased the half-life of yolk RBP by 31%, while the other modifications decreased the half-life by as much as 60%. During a 10-day period following injection of ¹²⁵I-labeled yolk RBP, 5.9% of the labeled protein was recovered from egg yolk. Relative to native yolk RBP, the transport of asialo-yolk RBP was decreased by 82%. The other modifications resulted in even less transport to the egg, the lowest being glycosidase-treated asialo-yolk RBP which was decreased by over 99%. By comparison of samples with similar clearance times, a positive correlation was made between sialic acid and ovarian transport.     

Microdissection of the mouse egg

A rapid and efficient method for microdissection of the mouse egg is described. The dissection is carried out in hanging drops of medium surrounded by heavy liquid paraffin oil at room temperature. Eggs are first deformed into a cylindrical shape and then dissected at a predetermined site with a glass needle on a Leitz micromanipulator. The survival rate of the dissected fragments is 75–90% and between 20 and 30 eggs can be dissected in an hour. Development of the dissected eggs is at least as good as that described after other types of manipulation. Cytoplasts and karyoplasts of various sizes can be prepared, as well as gynogenetic and androgenetic eggs with different amounts of cytoplasm. This procedure may help to examine nuclear-cytoplasmic interactions in eggs reconstituted from a variety of fragments.