Effect of egg incubator temperature on sex differentiation in Korat chickens

The effect of incubator temperature on sex differentiation in Korat chickens was investigated. The experiments were divided into two sets: temperature applied throughout the entire incubation period and temperature applied during certain periods (days 3–6 of incubation) by either increasing above the standard or decreasing below the standard temperature. In each experiment, 300 Korat chicken eggs were separated into three groups of 5 repetitions, with 20 eggs in each group. This was done using a completely randomized design for each experiment: a group using a temperature below the standard for incubation (36.0 °C), a group using the standard incubation temperature (37.7 °C), and a group using a temperature above the standard for incubation (38.0 °C). W chromosomes were detected at hatch; histology examined reproductive structures after 35 days. Increasing the temperature to 38.0 °C throughout the entire incubation period resulted in no significant difference in hatching rates compared to the standard temperature (P > 0.05). Raising the temperature to 38.0 °C throughout the entire incubation and during certain periods resulted in changes in the reproductive structure of chickens, leading to a mismatch between chromosomal and gonadal sex, observed at 9.7% and 5.9% of individuals with W chromosomes possessed testes, indicating a mismatch between chromosomal and gonadal sex. However, decreasing the temperature to 36.0 °C throughout the incubation period resulted in lower hatching rates compared to the standard temperature (P < 0.05). Incubating eggs at 36.0 °C for specific periods resulted in 19.4% of genetic males developing ovaries instead of testes. The presence of ovaries in individuals without W chromosomes indicated this mismatch. The results of this study provide evidence that temperature plays a role in sex differentiation in Korat chickens, as demonstrated by the detection of W chromosomes and histological studies of testes and ovaries. Moreover, this study presents the first evidence in broilers that temperature can affect sex differentiation.