Microbiome formation and assemblage are essential processes influencing proper embryonal and early-life development in neonates. In birds, transmission of microbes from the outer environment into the egg's interior has been found to shape embryo viability and hatchling phenotype. However, microbial transmission may be affected by egg-white antimicrobial proteins (AMPs), whose concentration and antimicrobial action are temperature-modulated. As both partial incubation and clutch covering with nest-lining feathers during the pre-incubation period can significantly alter temperature conditions acting on eggs, we experimentally investigated the effects of these behavioural mechanisms on concentrations of both the primary and most abundant egg-white AMPs (lysozyme and avidin) using mallard (Anas platyrhychos) eggs. In addition, we assessed whether concentrations of egg-white AMPs altered the probability and intensity of bacterial trans-shell penetration, thereby affecting hatchling morphological traits in vivo. We observed higher concentrations of lysozyme in partially incubated eggs. Clutch covering with nest-lining feathers had no effect on egg-white AMP concentration and we observed no association between concentration of egg-white lysozyme and avidin with either the probability or intensity of bacterial trans-shell penetration. The higher egg-white lysozyme concentration was associated with decreased scaled body mass index of hatchlings. These outcomes demonstrate that incubation prior to clutch completion in precocial birds can alter concentrations of particular egg-white AMPs, though with no effect on bacterial transmission into the egg in vivo. Furthermore, a higher egg white lysozyme concentration compromised hatchling body condition, suggesting a potential growth-regulating role of lysozyme during embryogenesis in precocial birds.

• Keywords
• Albumen, Antimicrobial proteins, Bacterial penetration, Embryo viability, Incubation, Microorganisms, Temperature,
• Publication type
• Journal Article MeSH

Eggshell colour, quality, and biosafety of table eggs are of significant commercial interest. To date, there have been few studies investigating the relationship between eggshell pigmentation and internal egg quality in commercially bred birds. Moreover, the genetic basis and mechanisms behind the effects of extrinsic factors on deposition of antimicrobial compounds in egg white and eggshell pigments are not fully understood. In the present study, we evaluate the effect of chicken breed identity, eggshell pigmentation and the role of extrinsic factors (year and breeder identity) on variability in the concentrations of 2 major egg white antimicrobial proteins (AMPs), lysozyme (LSM), and ovotransferrin (OVOTR), across 23 traditional chicken breeds. We found that chicken breed identity and eggshell pigmentation explained most variability in the concentration of egg white LSM and OVOTR. Year and breeder identity were also significant predictors of egg white LSM and OVOTR variability, and showed selective effects on the deposition of both AMPs in egg white. We also documented a positive correlation between concentration of egg white LSM and eggshell cuticle protoporphyrin in tinted and dark brown eggs, but not in brown, white, and blue eggs. We assume that a combination of both intrinsic genetic and hormonally regulated extrinsic factors is responsible for this relationship and for the variability in egg white AMPs. In this study, we demonstrate the existence of a relationship between eggshell pigmentation and egg white AMPs content in the eggs of traditional chicken breeds that may advertise the egg's antimicrobial potential and biosafety. These findings provide novel insights into the relationship between eggshell pigmentation and egg internal quality and may stimulate the recovery and exploitation of traditional chicken breeds for egg production, where the demands for egg quality and biosafety, in conjunction with animal welfare, are a priority.

• Keywords
• albumen, eggshell colour, lysozyme, ovotransferrin, protoporphyrin IX,
• MeSH
• Immunomodulation genetics   MeSH
• Antimicrobial Cationic Peptides genetics   metabolism   MeSH
• Chickens genetics   immunology   metabolism   MeSH
• Pigmentation MeSH
• Avian Proteins genetics   metabolism   MeSH
• Egg Shell chemistry   MeSH
• Egg Proteins genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antimicrobial Cationic Peptides MeSH
• Avian Proteins MeSH
• Egg Proteins MeSH