The estimation of endogenous excreta and the measurement of metabolisable energy in poultry feedstuffs using four feeding systems, four assay methods and four diets

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Abstract
1. Four different methods (dual semi‐quick (DSQ), conventional, a true metabolisable energy (ATM) method and Farrell's rapid method) were used to measure in adult roosters the apparent metabolisable energy (AME) and true metabolisable energy (TME) of four maize‐based diets with bran inclusions of 0, 200, 400 and 600 g/kg 2. Daily food intakes per bird were 75 g (or ad libitum) (H), 35 g (M) and 10 g (L). AME values determined by DSQ, conventional and Farrell methods were not different at the two highest intakes but were depressed at L intakes. ATM method often gave different values from other methods, particularly at the lowest intake. 3. The linear relationships between food intake and excreta energy yielded intercept values of 13 to 32 kJ/d for three methods; but ATM method yielded intercepts of 31 to 52 kJ/d. In a separate experiment it was demonstrated that a linear model may not be the most appropriate fit to such data. Removal of data for the 10 g/d intake yielded linear regression equations with intercepts not significantly different from zero for the two continuous feeding methods (i.e. a zero estimate for endogenous urinary and metabolic faecal energy (EEL), but for the two methods using a single input after fasting, intercepts were almost always positive. This confirms Härtel's (1986) observation of the absence of EEL under continuous feeding but its ever presence using a TME assay. 4. Correction of AME for EEL to obtain TME tended to increase values for all diets and also within a diet with decreasing intakes. The effect of correcting AME to nitrogen balance (n) was to give AMEn values that were more consistent between diets and reduced differences between methods. For the conventional method differences between the three intakes on all diets were greatly reduced. 5. There is reason to be concerned about the many different metabol‐isable energy values obtained using the ATM method compared to the three other methods and the basis for correcting for endogenous excreta. It is concluded that because of the uncertainty of EEL values, their variation and application, the AME system should be retained.