Maintenance energy requirements of laying hens: a comparison of measurements made by two methods based on indirect calorimetry.

1. The aims of this study were to compare maintenance metabolisable energy requirement estimates obtained in laying hens by two methods of respiration calorimetry, to investigate the changes in the heat production and energy retention of laying hens associated with temporarily reduced energy intake and to demonstrate the errors caused by using inappropriate values of net efficiency of energy utilisation (k) when extrapolating to maintenance energy requirement from a range of energy retention values. 2. One of the methods used regression of a range of energy retentions on energy intakes, followed by interpolation of zero energy retention; the other method employed extrapolation to zero energy retention from a single level of energy intake and retention. 3. Maintenance energy requirements derived from the two methods were similar. There was no indication that repeated temporary reduction of energy intake for the regression method gave a reduced value for maintenance energy requirement. The main potential advantage of the single-point method is therefore rapidity. 4. The single-point method relies for accuracy either on fixing an energy intake near the expected maintenance or on having a very accurate value for k. For example, the error attributable to using an assumed net efficiency (k) value of 0.7 when the true value was 0.8 was shown to vary between 0 if energy retention was measured at the equilibrium point and about 70 kJ/kgW0.75 d, or +15%, if energy retention was measured in the fasted state. 5. Stability of heat production and energy intake was approached after 2 d of reduced energy intake.