Background: Food is an important environmental factor that affects animalsâ?? energy metabolism and food shortage\nhas significant effects on animalsâ?? behavior, physiology and biochemistry. However, to date few studies have focused\non the thermogenesis and its effects on the body condition of birds. In this study, we examined the effects of food\nrestriction on the body mass, basal metabolic rate (BMR) and body composition, and several physiological, biochemical\nand molecular markers potentially related to thermogenesis, in the Chinese Bulbul (Pycnonotus sinensis).\nMethods: Birds in the control group were provided with food ad libitum whereas those in the food restriction group\nwere provided with one-half of the usual quantity of food for 12 days. Oxygen consumption was measured using an\nopen-circuit respirometry system. Mitochondrial state 4 respiration and cytochrome c oxidase (COX) activity in the\nliver and pectoral muscle were measured with a Clark electrode. Avian uncoupling protein (avUCP) mRNA expression\nwas determined in pectorals muscle with quantitative Real-time PCR.\nResults: Chinese Bulbuls in food restriction group decreased in body mass, BMR and internal organ (heart, kidneys,\nsmall intestine and total digestive tract) mass compared with the control group over the 12-day period of food\nrestriction. Bulbuls in the food restriction group also had lower levels of state-4 respiration, COX activity in the liver\nand muscle, and mitochondrial avUCP gene expression in muscle compared to the control group. BMR was positively\ncorrelated with body mass, state 4 respiration in the liver and COX activity in the muscle.\nConclusions: Our data indicate that Chinese Bulbuls not only sustain food shortage through simple passive mechanisms,\nsuch as reducing body and organ mass and energy expenditure, but also by reducing energetic metabolism in\nthe liver and muscle.
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