We say “as alike as two eggs”, and yet hens’ eggs come in a whole range of colours, shapes and sizes. The ones from grandma have yolks that are “somehow yellower than the ones from the shops”, and the neighbour’s over the fence seem bigger. But it is not just about first impressions: eggs can also differ in what lies beneath the shell, in their composition.
The Czech Gold Brindled Hen and the Oravka are Czech and Slovak national breeds that have been bred and kept for centuries. And it was these two breeds that the scientists chose for their research. They compared the influence that breed, housing system and hen age can have on the quality of the eggs laid. They looked, for example, at egg weight and shape, shell strength and colour, the yolk to albumen ratio, and also at blood indicators such as total cholesterol and protein content in the blood.
The scientists assessed eggs from hens aged 34, 42 and 50 weeks kept in so-called enriched cages and in litter-based systems. A total of 132 birds were used in the study, and 60 eggs were collected from each breed at each point during the monitoring period. Blood samples were also taken from the laying hens themselves, from the wing vein between seven and eight o’clock in the morning.
So what did the results show? The scientists found significant differences, for example, in blood cholesterol levels, which were higher in hens kept in enriched cages. Differences in total protein content, on the other hand, were related to the age of the hens, with younger hens having higher levels in their blood. As for egg quality, shell colour was influenced mainly by breed, while the housing system affected shell weight, surface, thickness and strength. The results provide an interesting comparison of changes in blood biochemical parameters and egg quality. These factors certainly need further research, especially in other breeds, for which such data are unfortunately often still lacking.
You can find the original paper here:
www.sciencedirect.com/science/article/pii/S0032579120307926
Kraus, A., Zita, L., Krunt, O., Härtlová, H., & Chmelíková, E. (2021). Determination of selected biochemical parameters in blood serum and egg quality of Czech and Slovak native hens depending on the housing system and hen age. Poultry Science, 100(2), 1142-1153.
Ing. Adam Kraus
Co-author
After completing a master’s degree specialising in the Quality and Processing of Agricultural Products, he has been pursuing doctoral studies at the Department of Animal Husbandry since 2018. At the faculty, he teaches meat processing technology. In 2019 he completed an internship abroad at the National Research Institute of Animal Production in Kraków. He publishes actively and takes part in conferences focusing on the performance and production quality of laying hens.