Development of Chicken Embryos in Double-Yolk Eggs: Fertility, Hatchability, Embryo Malposition and Time of Embryonic Mortality

Simple Summary: Due to lower parameters such as fertility rate and hatchability rate in comparison with single-yolk eggs, double-yolk eggs are not used for incubation in commercial poultry production. For this reason, double-yolk eggs are rarely the subject of research, and knowledge of embryonic development in this type of egg remains scarce. In this study, three types of chicken eggs (single-yolk eggs, double-yolk eggs with one developing embryo, and double-yolk eggs with two developing embryos) were compared in terms of embryonic mortality during incubation and chick quality. Embryonic mortality differed between single-yolk and double-yolk eggs at all stages of incubation. In the case of double-yolk eggs, embryonic mortality did not differ only in the initial stage of incubation. Despite the fact that two embryos in a single egg during incubation developed to a fairly advanced stage, no chicks were obtained from this type of egg. No differences were shown in chick quality between chicks from single-yolk eggs and double-yolk eggs with one developing embryo, but the weight of chicks from double-yolk eggs was significantly higher. Embryo malposition was more common in double-yolk eggs with two developing embryos. The study contributes to knowledge of embryo development and mortality in double-yolk eggs. Fertility rate and hatchability rate are low for all types of double-yolk (DY) eggs in comparison to single-yolk eggs (SY), but these parameters also depend on the number of developing embryos in the egg. The hatchability rate of double-yolk eggs containing two developing embryos (DY2F) is vastly lower than in the case of double-yolk eggs containing only one embryo (DY1F). The aim of the study was to determine the differences between egg fertility rate, hatchability rate, time of embryonic mortality, and embryo malposition during incubation in three types of eggs from Hy-Line Brown hens: SY, DY1F and DY2F. In addition, the quality of the hatched chicks was assessed using the Pasgar (c) score. Following a 21-day incubation, chicks were obtained from DY1F and SY eggs. No chicks were obtained from DY2F eggs, although the embryos in these eggs developed up to the late stage of incubation. Early (<= 7d of incubation), middle (8-14 d), and late (>= 15d) embryonic mortality was significantly higher in DY eggs than in SY eggs. The embryonic mortality rate during early incubation was the same for DY1F and DY2F eggs, but middle and late embryonic mortality were significantly higher for DY2F eggs. Based on evaluation of embryo position according to Landauer, only three types of malposition that could potentially lead to embryonic death were noted. There were fewer malpositioned embryos in double-yolk eggs containing one embryo. Quality assessment of chicks (Pasgar (c) score) showed no differences between chicks hatched from eggs containing one yolk and those hatched from double-yolk eggs with one developing embryo, but chicks from double-yolk eggs were significantly heavier. The results of the research will contribute to a better understanding of the development and mortality of embryos in double-yolk eggs.