Evaluation of sex differences in embryonic heart rates

Adult female chickens are known to have higher heart rates than adult males. Previous evidence suggested that sex-related differences in heart rates exist in embryos. The objective of the present study was to determine if differences in heart rate can be used for sexing chickens during embryonic development. The effects of hyper and hypothermia also were evaluated. On Day 14 of incubation, Single Comb White Leghorn embryos were candled and three surface electrodes were placed on the eggshell. The electrodes were attached to an electrocardiograph. Heart rates were recorded from Days 15 to 20 of incubation. Female embryos exhibited higher mean heart rates than males (2 to 4 beats/min) for Days 15 to 19 of incubation. Average heart rates of male and female embryos decreased and were significantly different when exposed to hypothermia (26.1 C for 2 h) on Day 15 of incubation. Hyperthermia (39.4 C for 45 min) on Day 15 of incubation increased embryonic heart rates, but male and female heart rates did not differ significantly. Extensive overlap between male and female heart rates under normal and hypothermic conditions makes this technique an industrially impractical method for determining embryonic sex.