In the past 50 years, selection starting initially at the breed level and then using quantitative genetics coupled with a sophisticated breeding pyramid, has resulted in a very productive hybrid for a variety of traits associated with egg production.One major trait currently being developed further is persistency of lay and the concept of the “long life” layer. Persistency in lay however cannot be achieved without due consideration of how to sustain egg quality and the health and welfare of the birds in longer laying cycles. These multiple goals require knowledge and consideration of the bird’s physiology, nutritional requirements, which vary depending on age and management system, reproductive status and choice of the selection criteria applied.The recent advent of molecular genetics offers considerable hope that these multiple elements can be balanced for the good of all in the industry including the hens.The “long life” layer, which will be capable of producing 500 eggs in a laying cycle of 100 weeks, is therefore on the horizon, bringing with it the benefits of a more efficient utilisation of diminishing resources, including land, water, raw materials for feed as well as a reduction in waste, and an overall reduced carbon footprint.

Avian influenza viruses are considered to be key contributors to the emergence of human influenza pandemics. A major determinant of infection is the presence of virus receptors on susceptible cells to which the viral haemagglutinin is able to bind. Avian viruses preferentially bind to sialic acid α2,3-galactose (SAα2,3-Gal) linked receptors, whereas human strains bind to sialic acid α2,6-galactose (SAα2,6-Gal) linked receptors. While ducks are the major reservoir for influenza viruses, they are typically resistant to the effects of viral infection, in contrast to the frequently severe disease observed in chickens. In order to understand whether differences in receptors might contribute to this observation, we studied the distribution of influenza receptors in organs of ducks and chickens using lectin histochemistry with linkage specific lectins and receptor binding assays with swine and avian influenza viruses. Although the intestinal epithelial cells of both species expressed only SAα2,3-Gal receptors, we found widespread presence of both SAα2,6-Gal and SAα2,3-Gal receptors in many organs of both chickens and ducks. Co-expression of both receptors may allow infection of cells with both avian and human viruses and so present a route to genetic reassortment. There was a marked difference in the primary receptor type in the trachea of chickens and ducks. In chicken trachea, SAα2,6-Gal was the dominant receptor type whereas in ducks SAα2,3-Gal receptors were most abundant. This suggests that chickens could be more important as an intermediate host for the generation of influenza viruses with increased ability to bind to SAα2,6-Gal receptors and thus greater potential for infection of humans. Chicken tracheal and intestinal epithelial cells also expressed a broader range of SAα2,3-Gal receptors (both β(1-4)GlcNAc and β(1-3)GalNAc subtypes) in contrast to ducks, which suggests that they may be able to support infection with a broader range of avian influenza viruses.

Novel and traditional eggshell quality measurements were made from up to 2000 commercial pedigree hens for a candidate gene association analysis with organic eggshell matrix genes: ovocleidin-116, osteopontin (SPP1), ovocalyxin-32 (RARRES1), ovotransferrin (LTF), ovalbumin and ovocalyxin-36, as well as key genes in the maintenance and function of the shell gland [estrogen receptor (ESR1) and carbonic anhydrase II (CAII)]. Associations were found for (i) ovalbumin with breaking strength and shell thickness; (ii) ovocleidin-116 with elastic modulus, shell thickness and egg shape; (iii) RARRES1 with mammillary layer thickness; (iv) ESR1 with dynamic stiffness; (v) SPP1 with fracture toughness and (vi) CAII with egg shape. The marker effects are as large as 17% of trait standard deviations and could be used to improve eggshell quality.

The cuticle is a proteinaceous layer covering the avian egg and is believed to form a defence to microorganism ingress. In birds that lay eggs in challenging environments, the cuticle is thicker, suggesting evolutionary pressure; however, in poultry, selection pressure for this trait has been removed because of artificial incubation. This study aimed to quantify cuticle deposition and to estimate its genetic parameters and its role on trans-shell penetration of bacteria. Additionally, cuticle proteins were characterised to establish whether alleles for these genes explained variation in deposition. A novel and reliable quantification was achieved using the difference in reflectance of the egg at 650 nm before and after staining with a specific dye. The heritability of this novel measurement was moderate (0.27), and bacteria penetration was dependent on the natural variation in cuticle deposition. Eggs with the best cuticle were never penetrated by bacteria (P < 0.001). The cuticle proteome consisted of six major proteins. A significant association was found between alleles of one of these protein genes, ovocleidin-116 (MEPE), and cuticle deposition (P = 0.015) and also between alleles of estrogen receptor 1 (ESR1) gene and cuticle deposition (P = 0.008). With the heritability observed, genetic selection should be possible to increase cuticle deposition in commercial poultry, so reducing trans-generational transmission of microorganisms and reversing the lack of selection pressure for this trait during recent domestication.

1. The avian eggshell is a biomineralised composite ceramic consisting of calcium carbonate embedded in an organic matrix. Matrix components are supposed to be involved in the control of mineralisation, crystallographic texture and biomechanical properties of eggshell. 2. The structure and eggshell matrix composition of various domesticated bird species were compared to gain insight into the universality of the eggshell mineralisation process. 3. The SDS-PAGE profiles of soluble eggshell matrix were specific within groups of birds (a: laying hen, breeder hen, quail, pheasant and possibly turkey; b: guinea fowl; c: duck and goose) but some of the protein bands were common to all groups. 4. Analogies between species were confirmed by Western blotting using hen protein antibodies. Ovocleidin-17 (OC-17) and ovalbumin were revealed in all species (except quail for OC-17). Lysozyme was present only in hen eggshell. Another egg white protein: ovotransferrin showed a positive signal in hens, turkey and quail. Osteopontin was observed in laying and breeder hens and quail. 5. Different proteoglycans were localised to discrete regions within the eggshell. Dermatan sulphate was observed within the matrix of the calcified shell of all species except quail which contained chondroitin-6-sulfate. Keratan sulphate was observed in mammillary bodies of breeder and laying hen, quail, pheasant and turkey while chondroitin sulphate was also present in guinea fowl and duck. 6. The general structural organisation of the different avian eggshells was similar but specific differences were observed in the ultrastructure of the mammillary layer. Species of the same taxonomic family could be grouped according to their structural analogies: breeder hen, turkey and pheasant resembled that of the domestic fowl. Guinea fowl was unique. Goose and duck were quite similar with large and confluent mammillary bodies. 7. Some matrix components are therefore common to eggshells of various species but more information is needed to relate differences in matrix composition between taxonomic groups with differences in ultrastructure.