The Thyroxine Secretion Rate of Growing White Pekin Ducks

THE role of the hormone of the thyroid gland, thyroxine, is becoming better appreciated by poultrymen as a result of the extensive experimental work being conducted with fowls concerning the effect both of mild hyper- and hypothyroidism. This work has been made possible by the use of two new products, thyroprotein and thiouracil, which may be incorporated in the poultry rations to induce these two conditions. The experimental work in this field is beginning to show that certain strains of fowls show improvement in the growth and egg production rate when their normal thyroid secretion rate is increased from exogenous sources. Other strains may show less benefit. It has been suggested that these variations in responsiveness are due to the variation in the level of the normal thyroid secretion rate. If the fowls have an optimal normal thyroid hormone secretion rate, then the further increase in the available thyroxine will . . .