L-Thyroxine and Thyroid Stimulating Hormone Secretion Rates of Young Adult and Aged New Hampshire Hens.

Summary TSR's and TSH-SR's of 53 adult New Hampshire hens ranging from 1 to 4 years of age were determined. No significant changes of TSR or TSH-SR occurred with increasing age within these adult stages. These birds had a mean TSR of 0.94 ± .07 μlg of L-thyroxine/100 g bw and a mean TSH-SR of 3.8 ± 0.23 mμ of TSH/ 100 g bw during late winter when the temperature was controlled to a mean of 55°F. However, this level of thyroidal activity represents a depression when compared to available data on the immature growing fowl.