Effect of dietary protein and energy intakes on whole-body protein turnover and its contribution to heat production in chicks.

A factorial 3 x 3 experiment was conducted with chicks to investigate the effect of manipulating crude protein (N x 6.25) intake (CPI) and metabolizable energy intake (MEI) simultaneously, in the range low to high (including adequate) levels with regard to the respective requirements, on whole-body protein turnover and its contribution to total heat production. The fractional rate of whole-body protein synthesis was increased curvilinearly by increasing MEI or CPI from low to high levels. In terms of absolute rates whole-body protein synthesis was enhanced by increasing MEI from low to adequate levels, the effect being greater at adequate and high CPI than at low CPI. The effect of varying CPI and MEI on whole-body protein degradation was similar, but less sensitive, to that on whole-body protein synthesis. Increasing MEI from low to high levels elevated total heat production at all CPI levels. There were no interactive effects of varying CPI and MEI on the contribution of whole-body protein synthesis to total heat production, and in general the contribution increased with increasing CPI and decreased with increasing MEI. The contribution of whole-body protein synthesis to total heat production fell within a small range from 11.2 to 16.5%.