Estimation of Thyroid-Stimulating Hormone (TSH) Secretion Rates of New Hampshire Fowls. ∗

Summary

A method of estimating the daily TSH-SR of fowls is described, depending on a comparison of the normal thyroidal-I131 release rate where recycling of I¹³¹ is blocked by a goitrogen, endogenous TSH release is blocked with thyroxine at the TSR level and by producing a comparable thy-roidal-I¹³¹ release rate with the daily subcutaneous injections of TSH assayed against a USP Reference Standard TSH. TSR and TSH-SR of 2-year-old New Hampshire hens were shown to be significantly higher during late spring than during late summer to early fall. No significant difference was observed between TSR and TSH-SR of 1-year-old and 2-year-old hens tested concurrently during late summer. However, there was no significant correlation between TSR and TSH-SR of these hens.