Implications and development of a net energy system for broilers

A study was conducted to determine the predictability of energy balance and energy efficiency by using dietary chemical composition. Closed-circuit indirect calorimetry was used to determine the apparent metabolisable energy (AME), respiratory quotient, heat increment (HI), net energy (NE) and ratio of NE to AME (NE : AME) of a series of diets with varying levels of chemical constituents. Diets were analysed for DM, gross energy, protein, fat, ash, crude fibre, acid detergent fibre, neutral detergent fibre, starch, sugars (mono- and disaccharides), and soluble, insoluble and total non-starch polysaccharides. Ross 308 male broilers were acclimatised to chambers and diets for 3 days and 12 days, respectively, before O₂ consumption and CO₂ expiration were measured gravimetrically. Gross energy of feed consumed and excreta voided were measured and AME was calculated. Heat production was calculated using the Brouwer equation based on O₂ and CO₂. After taking fasting heat production into account by using a value of 450 kJ/BW⁰˙⁷⁰, HI was determined. NE was calculated as AME minus HI. The results showed high predictability of AME (R² = 0.89) and NE (R² = 0.85) by using chemical components. HI was less predictable (R² = 0.25). Efficiency of energy utilisation (NE : AME) was predicted (R² = 0.40). Closed-circuit calorimetry was found to be useful for evaluating the contribution of the chemical components of feed ingredients to the efficiency of energy utilisation in broilers. These results may be used to reduce energy costs in broiler feed formulation.