EN
It has been established that 3.3’, 5-triiodothyronine (Тз) acts hipermetabolically, whereas 3’3.5’-triiodothyronine (reverse Тз, гТз) acts hypometabolically. The normal ratio of Тз to гТз in domestic fowls fluctuates around 10. Since the excess of Тз may promote catabolic processes and lower weight gain, the aim of this experiment was to find the optimal ratio of Тз:гТз in blood plasma which corresponds with the greatest weight gain in Japanese quail. Reverse Тз was given in drinking water (1 pg гТз/ml) for 3, 10, 20 or 30 days. It has been found that Тз/гТз ratio of about 5, after 20 days of гТз administration, stimulated the weight gain of Japanese quail of both sexes from 7 to 44% with more pronounced effect in female birds.