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1. Two experiments were carried out to investigate the influence of substitution levels, assay methods and adaptation length of broilers to experimental diets on metabolisable energy of corn and barley (Experiment 1) and soya bean meal (Experiment 2). In each experiment, the test feedstuffs proportionately replaced the reference diet at the rates of 150, 300 or 450 g/kg. Each treatment had 8 or 7 replicate cages containing three birds per cage. Broiler chickens were adapted to experimental diets for either 7 or 4 d prior to excreta collection on d 20 and 21. 2. Metabolisable energy was determined using the difference method at each substitution level and the regression method, using the 4 combinations of the substitution levels. 3. In Experiment 1, AME and AMEn were lower (P < 0.01) for barley than for maize, irrespective of the assay method and there was a trend for an adaptation × cereal grains interaction (P < 0.10) for AME determined by the difference regression method. For maize, AME and AMEn calculated using regression or the difference method were not significantly different, whereas barley AME and AMEn values were greater (P < 0.01) when derived using regression analysis. 4. In Experiment 2, there was no significant adaptation length × substitution levels interaction. The AME and AMEn values were lowest (P < 0.01) at 150 g/kg SBM inclusion level when calculated using the difference method. On the other hand, AME and AMEn values determined by the regression method were not influenced by substitution levels. 5. It was concluded that the influence of substitution levels on assayed metabolisable energy is feedstuff-dependent and that the regression method produced more consistent metabolisable energy values in a feedstuff-independent manner. [ABSTRACT FROM AUTHOR]

1. Changes in feather length and weight and daily losses of down, contour feathers, remiges and retrices were studied in two commercial broiler strains to determine feather growth and moult in broilers up to 112 d of age. 2. Ten pens of 20 chicks for each sex x strain were fed adequate amounts of dietary protein in a four-phase feeding programme. Ten birds were sampled per genotype at 14, 28, 42, 56, 70, 84, 98 and 112 d. Feather loss was determined for individual birds caged within a nylon net. 3. All feathers were dry-plucked from each of seven tracts, with representative feathers from the capital-cervical, dorsopelvic and interscapular, pectoral and femoral tracts being randomly selected. Three rectrices of the dorsocaudal tract and three primaries and secondaries of the humeral-alar tract of the right wing were evaluated. 4. The length of the selected feathers was measured, and the feathers from each tract and from the whole bird were weighed. 5. A wide range of rates of maturing (0.0250–0.0907/d) and mature weights (9.62–52.9 g) were evident between sampled tracts. 6. Feather weight failed to predict some moults which were detected by the measurement of feather losses. From the weight data, moulting was evident only in the humeral-alar and dorsocaudal tracts, whereas, when daily losses were measured, contour feathers accounted for over 0.7 proportion of feather losses. Logistic equations adequately described the cumulative losses of down, contour feathers and remiges. 7. Feather loss needs to be considered when feather growth is determined from feather weight at different ages. 8. The rate of maturing (B) of feathers was numerically higher in Ross males and females than in the Cobb strain. In females, B was higher than in males (0.0483 vs. 0335/d) but the mature weight was lower (162 vs. 230 g). [ABSTRACT FROM AUTHOR]