Experiments were conducted to study the effects of thyroid hormone on growth and feed consumption. Male chicks were thyroidectomized at 15-days old and subjected to the intramuscular injection of L-thyroxine at levels of 0.5, 1.5 and 2.5 μg per 100 g of body weight per day for a 19-day period from the next day of the thyroidectomy. Autotransplantation of the thyroid glands was conducted by imbedding them in the subcutaneous tissue of the posterior region of the neck at 15-days old. The body weight and feed consumption were measured once a day for a 20-day period and a 19-day period, starting at 16-days old and 17-days old, respectively. A histological examination of the thyroid glands autotransplantated at 16-days old was carried out to determine the histological changes during the experimental period. The results obtained were summarized as follows: Body weight gain and feed consumption were adversely affected by the thyroidectomy when compared to the control (sham operation), while the decrease in body weight gain and feed consumption was prevented by the daily injections of 1.5 and 2.5 μg Lthyroxine except 0.5 μg. However, autotransplantation of the thyroid glands resulted in decreased body weight gain and feed consumption as compared to the control. Under the condition of this experiment, most of the follicles of the thyroid glands autotransplanted disappeared within 2 days following treatment and then regeneration of some follicles was observed, subsequently increased the number and size of the follicles with the lapse of time but never attained to the normal state as observed in the control.
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