Influence of dietary non-protein energy intake on whole-body protein turnover in chicks

1. Three experiments were conducted to investigate the influence of dietary energy intake on whole-body protein turnover in chicks. 2. In Expt 1 a semi-purified diet with various dietary metabolizable energy (ME) concentrations, 10.9, 12.6, 14.2 and 15.9 kJ/g, was fed ad lib. to young chicks. Whole-body fractional synthesis rate (FSR) was increased with each increment in dietary ME level from 12.6 to 15.9 kJ/g, and whole-body fractional degradation rate (FDR) showed a similar, though less sensitive, trend to that of FSR. 3. In Expts 2 and 3, chicks were given graded ME intakes of 84, 126, 167, 209 or 293 kJ/d with a fixed intake of dietary protein. FSR was increased when the energy intake was raised from 84 to 167 kJ/d, and above this level it was almost constant. Similar to the trend obtained with ad lib. feeding, the response of FDR to changes in dietary energy intake was less sensitive than that of FSR. 4. Total heat production was increased when dietary energy intake was increased from 84 to 167 kJ/d, and there was no further increase at 209 kJ/d. In contrast, the contribution of protein synthesis to total heat production was not affected by varying the dietary energy intake.