Seasonal Variation in Thyroxine Secretion Rates in Two Strains of New Hampshire Chickens

STUDY of the thyroxine secretion rate of dairy cattle in Missouri has indicated considerable variation in rate due to seasonal change in environmental temperature. During the summer months, the mean secretion rate was only 1/3 that of the winter rate (Premachandra et al., 1958a). In fowls, the thyroxine secretion rate of two strains of New Hampshire chickens selected for high and low response to thiouracil during the winter months has been reported (Premachandra et al., 1958b). It was noted that the strain showing a marked response to thiouracil (high line) secreted a mean of 1.01 μg./100 g. body weight, whereas the strain showing low response secreted an average of 2.97 μg./100 g. body weight. Comparable data showing mean and range in thyroxine secretion rate of these two strains during the summer months are reported. EXPERIMENTAL The description of the two strains of New Hampshire chickens used in this study has …