Abstract:Thyroid hormones (thyroxine T4 and triiodothyronine T3) are unique in their ability to stimulate basal thermogenesis for small birds. The present study aims to examine the effect of thyroid hormones on thermogenesis in hyperthyroid Chinese bulbuls (Pycnonotus sinensis) that was fed T4 laced poultry food for 3 weeks. Birds were housed at room temperature (18-26℃). The rate of oxygen consumption was measured using the closed-circuit respirometer. The mitochondrial protein contents were determined by the Folin phenol method with bovine serum albumin as a standard. Respiration of liver and muscle mitochondria were measured polarographically at 30℃ in the presence of succinate using an oxygen electrode units (Hansatech Instruments Ltd., English). The activity of cytochrome C oxidase (COX) was also determined polarographically at 30℃. Chinese bulbuls fed on T4-laced poultry food showed increases in basal metabolic rate (BMR) during 3-week acclimation. Finally, these bulbuls had higher levels of mitochondrial protein contents in muscle, state 4 respiration and COX activity in liver and muscle and serum T4 and T3 contents than that of control bulbuls. These results provide support for the hypothesis that thyroid hormones play an important role in the regulation of thermogenic ability by stimulating mitochondrial respiration and enzyme activities associated with aerobic metabolism.