The effect of thyroidectomy on testicular size and on the photorefractory period in the starling (<i>Sturnus vulgaris</i> L.)

Abstract

Abstract Thyroidectomy of Starlings prior to exposure to long photo‐periods (17L:7D) resulted in a failure of testes to regress after an initial size increase. Thyroidectomy after four weeks of such exposure resulted in testicular regression followed by a second period of size increase. Testicular size was correlated with androgen secretion as indicated by yellowing of the bill. The effect of thyroidectomy was not due to increased gonadal sensitivity to gonadotrophins and not due to the requirement of the presence of the thyroid for regression per se . Presumably thyroidectomy results in higher gonadotrophin secretion. Thyroidectomy did not affect the termination of the photorefractory period in the fall. Thyroidectomized Starlings had higher body weights than controls.