Sex-biased mortality analysis in chick embryos during the entire period of incubation

SUMMARY From 50,129 fertile eggs, a total of 1,712 dead chick embryos were collected from 5 different strains of chickens: ai-Jiao (233), Xing-Xing (143), HuBei-local (894), Hy-line (212), and Zhu-Si (230). the embryos were collected during the early (1 to 7 d), middle (8 to 14 d), and late (15 to 21 d) stages of incubation. Sex-biased embryonic mortality was analyzed during the different stages. We found that the overall mortality of female embryos was significantly higher than that of males in different stages of incubation (P < 0.05). We then analyzed the data by strain. In Hy-line, HuBei-local, and Zhu-Si chickens, female mortality was significantly higher (P < 0.05) during the early stage. During the middle stage, female mortality in HuBeilocal chickens was significantly greater than that of males (P < 0.005). During the late stage, female mortality was significantly lower (P < 0.05) in ai-Jiao chickens but was significantly higher (P < 0.01) in HuBei-local chickens. thus, more females died during the entire period of incubation, especially in the early and middle stages. Mortality was variable among strains during the late stage of incubation. In strains with smaller egg sizes, more females died, whereas in strains with larger egg sizes, more males died.