Energy and nitrogen intake, expenditure and retention at 20° in growing fowl given diets with a wide range of energy and protein contents

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Abstract
Heat production (HP) and the intake and retention of energy and nitrogen were measured at 20° in growing female broiler fowl given diets with metabolizable energy (ME) contents ranging from 8 to 15 MJ/kg at each of two crude protein (nitrogen × 6.25; CP) contents (130 and 210 g/kg). ME intake was partially controlled by the birds, but increased by 30% over the range of dietary ME concentration. CP intake varied directly with dietary CP:ME ratio, indicating that control of energy intake took priority and that food intake did not increase in order to enhance amino acid intake on low-CP diets. Maintenance energy requirement and fasting HP were not affected by diet. Although the HP of fed birds was significantly affected by dietary energy source, there was no evidence for regulatory diet-induced thermogenesis as energy intake increased. Total energy retention doubled on the higher-energy diets as a result of increased intake and retention efficiency in the absence of any compensation by diet-induced thermogenesis. The proportion of energy retained as fat was negatively correlated with dietary CP:ME ratio. It was concluded that the growing female broiler fowl responded to large differences in energy intake and dietary CP concentration not by changes in rate of energy dissipation as heat but by changes in the quantity of energy retained and in the partition of retained energy between body protein and body fat.