Heart Rate of Chickens as Influenced by Age and Gonadal Hormones

Abstract

The average heart rate of the chick increases from 286 beats/min. at 1 day to 475 at 1 week, with the greatest change occurring during the first 3 days. Heart rate continues to increase slowly to a maximum of approximately 500 beats at 3–4 weeks, then declines gradually to a stable adult level between 280 and 350 at about 6 months. Between the 12th and 17 weeks, the heart rate of the male dropped 10–12% below that of the female, approximating the sex difference found in adults. Heart rate measurements on gonadectomized and gonadotrophin treated birds failed to indicate the role, if any, of gonadal hormones in the development of the sex difference in heart rate.