The Effect of Thyroprotein on Egg Production

EGG production in fowls follows a seasonal cycle. The early spring hatched chicks come into egg production in the fall, reach a plateau of production during the winter and early spring months, then begin to decline during the late spring and summer months (Dunn, 1924 Whetham, 1933). Egg production usually reaches a low level by late August or September as the hens begin to molt and subsequently grow new feathers. Variation in thyroid weight in chickens (Podhradský, 1935; Galpin, 1938) and pigeons (Riddle and Fisher, 1925) and in the iodine content of the chicken thyroid (Cruickshank, 1929) suggest a similar seasonal rhythm in thyroid activity; the rate of thyroid hormone secretion being at a low level in the summer and at a high level in the winter. This is further borne out by the course of change in fasting heat production with the season (Winchester, 1940). That environmental temperature is . . .