ABSTRACT: The basal metabolic rate in poultry, expressed as net energy requirements for maintenance (NEm), is often characterized by measuring fasting heat production (FHP) under standardized conditions. This study applies meta-analysis techniques to 206 individual observations from 23 peer-reviewed papers to evaluated the allometric relationship between FHP and body weight (BW), described by the model: FHP (kJ/d)=a×BW (kg)b , where FHP is the fasting heat production, BW is the body weight, a is the NEm requirement per unit of metabolic body weight (MBW), and b is the allometric exponent. The objective of this study was to estimate b and determine the appropriate NEm for growing broiler chickens, laying hens, and roosters. We evaluated three non-linear models: Model 1, category-specific exponents; Model 2, common exponent across categories; and Model 3, exponent fixed at the theoretically value of 0.75. Model 1 showed distinct b of 0.73, 0.65, and 0.58 for growing broilers, laying hens, and roosters, respectively, with corresponding NEm values of 450, 352, and 385 kJ per kg of MBW. Model 2, which estimated a common exponent (b = 0.64), improved model fit (root mean square prediction error (RMSPE) = 173 kJ/d, R 2 = 0.76). Model 3, using the standardized b = 0.75, yielded NEm of 478 kJ/kg BW0.75 for growing chickens and 320 kJ/kg BW0.75 for adult birds (RMSPE = 184 kJ/d, R 2 = 0.78), with a model performance comparable to Model 1 (RMSPE = 187 kJ/d, R 2 = 0.72). Error decomposition further indicated that Model 3 presented a lower error due to regression (0.66%), a lower intercept (80 kJ/d) and a higher slope (0.68) in the observed-predicted regression, demonstrating its robust predictive ability. In conclusion, while category-specific exponents offer a precise FHP characterization, adopting a wide-know exponent of 0.75 is a practical alternative, provided the NEm is adjusted for each category. These findings provided a framework for estimating NEm recommending values of 480 kJ/kg BW0.75 for growing chickens and 320 kJ/kg BW0.75 for adult birds, to support accurate energy requirements models and cross-study comparison in poultry nutrition.
