The impact of domestication process on eggshell microstructure in Gallus gallus, Anser anser and Anas platyrhynchos

The domestication process has had a substantial and varied impact on animals in terms of anatomy, physiology, and behaviour. Poultry species are particularly important for humans, with the most significant being chickens, geese, and ducks. However, it is not well understood whether, or to what extent selection influences the eggshell structure compared to wild ancestors. In the present study, we compared eggshells from three species: Red junglefowl and its four domesticated forms: Green-legged partridge, Lohmann Brown, Ko-Shamo, meat type breeder (Cobb 500); Greylag goose, and two domesticated breeds: Bilgoraj goose and White Koluda goose, as well as Mallard duck and domesticated crossbred KhO-01. The analyses revealed significant differences in the eggshell structure both between species (P < 0.001) and between breeds (P < 0.001 for chickens and geese, and P = 0.039 for ducks). Domesticated forms tend to have fewer mammillary knobs per mm2 (P = 0.004), which were larger (P < 0.001) and they show the smaller coverage of the mammillary knobs (P < 0.001). Analyses showed significant correlations of the body mass and egg size with eggshell characteristics (P < 0.001). Considering that domesticated forms are usually larger, it cannot be conclusively determined whether changes in structure result from the domestication process itself or are physiologically linked to body mass and egg size. The relatively high similarity between the eggs of the wild ancestor and the Ko-Shamo breed, which exhibits substantial morphological changes but has a body mass similar to that of the Red junglefowl, supports this interpretation.