Relation of Thyroxine Secretion Rate to Age and Growth Rate in the Cockerel

Abstract

IT IS well established that thyroid hormone increases basal metabolic rate in mammals and birds (Belasco and Murlin, 1941; McCartney and Shaffner, 1950). Basal metabolic rate is high in the young chicken and decreases with advancing age (Barott and Pringle, 1946). It has been reported that thyroxine secretion rate is higher in the young mice and chickens than in the adult ones (Hurst and Turner, 1948; Grad and Hoffman, 1955; Schultze and Turner, 1945). The present work was undertaken to elucidate the relationship of thyroxine secretion rate to age and to growth rate in the chicken. MATERIALS AND METHODSCockerels of White Leghorn (W.L.) and the crossbred between White Cornish males and White Leghorn females (W.C.×W.L.), bred at the National Institute of Animal Industry, were used. The birds hatched in early April were reared in electric brooders at 30°C. until 3 weeks of age and 25°C. until 9 weeks of…