The Effects of High Environmental Temperature on Thyroid Secretion Rate of Domestic Fowl

THERE is considerable evidence that the thyroid gland of birds responds to environmental temperature changes (Hoffman and Shaffner, 1950; Joiner and Huston, 1957; Premachandra et al., 1959; Heninger et al., 1960; Stahl and Turner, 1961). Studies have shown a relationship between thyroxine secretion rate and growth (Schultze and Turner, 1945; Glazener and Shaffner, 1948; Glazener et al., 1949; Hoffmann, 1950; Premachandra et al., 1958). Since growth rate and egg production are retarded by high environmental temperatures, an experiment was designed to measure the thyroid secretion rate of fowl of different ages exposed to different environmental temperatures. MATERIALS AND METHODS The birds used in all three trials were held from day of hatch in a room with a constant environmental temperature of either 66°F. or 88°F. All birds were grown in battery brooders until four weeks of age. Brooder temperatures were maintained at 95°F. the first week and dropped 5°F. each …