Maintenance Energy Requirement of Broilers and the Impact of Ambient Temperatures

Eight broiler weight groups, housed in metabolic chambers, were exposed to 3-5 ambient temperatures (AT) such that AT exposure fell below, near and above the projected thermoneutral (TN) zone. Birds were fed 0, 5, and 10% of body weight (W), or allowed to consume food ad libitum, to vary energy consumption. Energy needs for body weight homeostasis, efficiency of metabolizable energy (ME) use for maintenance and the exponent needed to convert live body weight to metabolic weight was estimated. Energy (Kcal W-1 d-1) and oxygen (l W-1 d-1) needs for body weight homeostasis declined curvilinearly as body weight increased from 0.042 kg to 2.44 kg. Such needs were impacted by AT. The efficiency of ME use to support maintenance energy need varied in a cubic fashion with bird mass. The estimated zone of thermoneutrality, at body weight homeostasis, was inversely related to W (kg), expressed as- TN (ºC) = 31.896 – 0.4625∙W (R2 = 0.99). Under metabolic basal rate (MBR) conditions, the TN zone was curvilinearly related to weight as- TNMBR = 32.6466 − (94.4603∙W) − (0.7660∙W2) (R2 = 0.99). The exponent, to linearize live body weight with heat production (HP) of birds fed to W homeostasis, was determined to be 0.758 with all birds strictly housed at TN. Further, the exponent to linearize HP of birds under MBR (fasted) conditions was estimated to be 0.679. Equations relating chick energy and oxygen consumption need with body weight and AT, metabolizable energy for gain homeostasis (MEmg), metabolizable energy for retained energy homeostasis (MEmr), metabolizable energy for protein homeostasis (MEmp), and metabolizable energy for fat homeostasis (MEmf) are presented.