Exploring the net energy for maintenance and the allometric exponent of the metabolic body weight in different categories of poultry: A meta-analyses approach

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. Variations in age, growth, and production status can influence both the allometric exponent and NEm, underscoring the need for accurate estimations specific to each poultry category. This study applies meta-analysis techniques to combine findings from 206 experiments, published in peer-review papers, conducted to estimate the allometric exponent and to determine NEm for growing broiler chickens, laying hens, and roosters. Rigorous analysis of the meta-design identified potential outliers and collinearity, ensuring the robustness of model selection. Three models were evaluated to assess differences in FHP across poultry categories: Model 1 considered unique allometric exponents for each bird category based on body weight (BW); Model 2 assumed a uniform allometric exponent across categories; and Model 3 fixed the exponent at the standard value of 0.75. Model 1 showed relatively lower predictiveness (root mean squared percentage error [RMSPE] = 0.502, r 2 = 0.77) and highlighted differences in the FHP and allometric exponents among categories, with values of 450 kJ/kg0.73 for growing broilers, 352 kJ/kg0.65 for laying hens, and 384 kJ/kg0.58 for roosters. Model 2, employing a single exponent (b = 0.64), improved model fit (RMSPE = 0.765, r 2 = 0.76), yielding FHP estimates of 491, 356, and 307 kJ/kg0.64 for growing broilers, laying hens, and roosters, respectively. Finally, Model 3, using the standardized exponent of 0.75, resulted in maintenance requirements of 478 kJ/kg0.75 for growing chickens and 320 kJ/kg0.75 for adult birds (RMSPE = 0.484, r 2 = 0.78), with comparable model performance than estimated by Model 1. Findings suggest that while the exponent 0.75 can be practically adopted, it still provides an accurate representation of metabolic scaling across poultry categories. This standardized approach supports practical applications and facilitates comparative studies in poultry nutrition and energy requirements.