Figure 3.

Conceptual nitrogen (protein) balance model (modified from Vogel et al. [61]) of body N concentrations (solid line) and BW (dotted line) against N and energy intakes in pigeons. a, pigeons in N balance when N and energy intakes are adequate to meet requirements; b, steady-state negative N balance when N intakes < N losses, however BW is maintained by adequate energy intakes; c, unsteady-state negative N balance when N loss relative to N intake continues to increase and/or energy intakes are unable to satisfy requirements so that tissue is lost and BW is not maintained. A, change from N balance, to steady-state negative N balance; B, change from steady-state negative N balance to unsteady-state negative N balance.