Effect of Synthetic Thyroprotein on Seasonal Variation in Volume and Concentration of Cock Semen

THERE has been considerable recent interest in the possibility of the thyroid gland being involved in the expression of seasonal reproductive rhythms in males. Parker and McSpadden (1942) and Wheeler and Andrews (1943) reported that cock semen quality and quantity was reduced during the summer months. Thyroid gland involvement in this decline may be inferred from the abundant evidence that thyroid activity is reduced when the ambient air temperature is increased (see below) and from the fact that summer sterility of rams may be improved by thyroxine or synthetic thyroprotein administration (Berliner and Warbritton, 1937; Bogart and Mayer, 1946). It is well known that temperature plays an important part in regulating thyroidal activity and that thyroid hormone is intimately concerned with gonadal activity. The controlling mechanism which regulates pituitary output of thyroid stimulating hormone (TSH), and indirectly the output of thyroid hormone (thyroxine), has been rather clearly outlined although much . . .