No evidence of temperature-dependent sex determination or sex-biased embryo mortality in the chicken

Skewing the sex ratio at hatch in commercial poultry would be economically beneficial to the poultry industry. The existence of temperature-dependent sex determination is uncertain in birds. This experiment investigated if incubation temperatures skew sex ratios of commercial broilers. Three incubators were each set at a hot (38.3°C), standard (37.5°C), or cool (36.7°C) single-stage incubation temperature one time over 3 trials to eliminate incubator effect as a Latin square design. Sex ratios of hatched chicks and dead embryos were monitored. In one trial, embryo weights were evaluated. The percentages of male hatched chicks did not differ based on incubation temperature (P = 0.4486; 49.5% in the hot treatment, 51.4% at standard temperature, and 49.8% in the cool treatment). The percent hatch of eggs set was lower in the hot treatment (83.6%) than the standard (93.5%) and cool (91.6%) treatments (P < 0.0001) with greater late embryonic mortality in the hot treatment (P < 0.0001); however, the sex ratio of dead embryos did not differ among treatments (P = 0.9863). Pooled data of embryo mortality found no sex-biased embryo mortality with a female/male sex ratio of 1.22:1 (χ(2) = 1.27; P = 0.2596). Embryos from the hot treatment were heavier than those from the standard treatment by d 14 of incubation and were heavier than the embryos from the cool treatment by d 9 of incubation (P < 0.0001). These data indicate that incubation temperature affects embryonic mortality and embryonic growth rate, but it does not affect the sex ratio of broiler chickens. Additionally, no evidence was found for sex-biased embryo mortality in commercial broilers even at the incubation temperatures of this study.