EN
The aim of this study was to assess the early embryonic development and hatchability of turkey eggs in relation to the age of layers. Analyses were performed at three-week intervals during a 24-week laying season. The first analysis was performed at week 33 of layers’ life (1st week of the laying season). The body conformation and development of embryos in the 64th hour of incubation, egg weight and hatching rates were determined at each stage of the study. The values of the blastodisc diameter were found to be higher in eggs laid by hens aged 45 weeks than in eggs laid by younger hens. Embryos in eggs from hens aged 39 weeks had a longer longitudinal axis and wider head region than in eggs laid by younger hens. The number of brain vesicles and somite pairs and the development of blood islands in embryos contained in eggs laid by hens aged 42 weeks and older were at a comparable level, while lower values were found in younger hens. The variation in embryo characteristics was high, which is typical of the early stage of embryo growth. Egg weight increased by 19.48 g between week 33 and 57 of layers’ life. The highest increase in egg weight was noted during the first 3 weeks of the laying season. The highest hatching rates (88.63-93.11%) were observed in the group of hens aged 39 to 48 weeks. The conducted research indicates that hatchability depends on the layer’s age, which determines the egg weight and embryonic development. A large increase of egg weight in the case of young hens and those at the end of their laying period caused a slower development of embryos and poorer hatchability.