Sex Ratio Bias in Early-Dead Embryos of Chickens Collected During the First Week of Incubation

According to Mendelian heredity laws, the sex ratio of a given chicken population during hatch- ing is expected to be 1:1. In this study, we collected 432 chicken embryos that died during the first week of incubation from 5 different breeds. The sexes of the early-dead embryos were determined by using the pre- viously described molecular sexing technique of double PCR. The female-to-male sex ratio was analyzed for departure from the expected 1:1 sex ratio by χ 2 testing. These results showed that the number of female dead embryos was significantly greater than that of males in the Hubei local breeding stock, Zhusi, and Hy-line Variety Brown (P < 0.05, P < 0.01, P < 0.01 respective- ly), with observed female-to-male sex ratios of 1.40:1, 2.03:1, and 2.22:1, respectively. Two other Chinese local breeds (the Yellow chicken and the Aijiaohuang chicken) also showed altered sex ratios, although the differences were not significant. Altogether, these re- sults indicated that female chickens were more likely than male chickens to die at the early stages of incuba- tion.