The impacts of hammer-mill screen size and grain particle size on the performance of broiler chickens offered diets based on two red sorghum varieties.

1. The two red grain sorghums were extensively characterised. Kafirin, polyphenolic compounds, free, conjugated and bound phenolic acids, phytate concentrations and starch pasting profiles were determined. 2. The experiment consisted of a 2 × 4 factorial array of dietary treatments comprising two red sorghum varieties (Tiger and Block I) ground through 4 hammer-mill screen sizes (2.0, 3.2, 4.8 6.0 mm) prior to incorporation into nutritionally equivalent diets. Eight steam-pelleted dietary treatments were each offered to 7 replicates (6 male Ross 308 birds per cage) from 7 to 28 d post-hatch. 3. Effects of dietary treatments on growth performance, relative gizzard and pancreas weights, nutrient utilisation, apparent starch and protein (N) digestibility coefficients and disappearance rates from 4 small intestinal segments were determined. 4. The 2.0-mm hammer-mill screen generated an average geometric mean particle size of 794 μm and the 6.0-mm screen a mean particle size of 1405 μm. However, hammer-mill screen size did not influence weight gain or FCR. The 6.0-mm screen size generated significantly higher starch and protein (N) digestibility coefficients in the distal jejunum and distal ileum than the 2.0-mm hammer-mill screen. 5. Tiger sorghum was superior to Block I sorghum, as significant advantages were observed for feed conversion ratios (3.25%), AME (0.37 MJ), ME:GE ratios (4.15%), AMEn (0.53 MJ), distal ileal starch digestibility coefficients (2.46%) and protein (N) digestibility coefficients in the distal jejunum (4.66%), proximal ileum (1.96%) and distal ileum (2.16%). The inferior Block I sorghum contained more kafirin (67.1 versus 51.3 g/kg), phytate (9.79 versus 8.40 g/kg), total phenolic compounds (4.68 versus 4.12 mg GAE/g), flavan-4-ols (7.98 versus 5.04 ABS/ml/g), total phenolic acids (554 versus 402 μg/g) and total ferulic acid (375 versus 281 μg/g) in comparison to Tiger sorghum.