Physical and nutritional effects of pelleting of broiler chicken diets made from wheat ground to different coarsenesses by the use of roller mill and hammer mill

Sammendrag

A study was conducted to assess the interactions between grinding, pelleting and broiler performance. A hard wheat was ground by the use of hammer mill fitted with a 3 or 6.1 mm sieve, or to the same geometric mean diameter by the use of a roller mill. Dry sieving revealed that the amount of particles smaller than 0.5 mm in size and larger than 1.6 mm in size was less with the roller mill than with the hammer mill. When diets containing 573.5 g ground wheat/kg were pelleted, wet sieving revealed that the proportion of fine particles smaller than 0.2 mm in size increased substantially. In addition, the pelleting process tended to even out differences in particle distribution between diets. No major differences in power consumption during pelleting were seen for the different diets. A somewhat poorer pellet quality in terms of breaking strength and resistance to abrasion was observed for diets made from coarsely ground wheat than for diets made from finely ground wheat. Extent of gelatinisation, measured by viscosity analysis and differential scanning calorimetry, varied between 1 and 19% and was inversely related to coarseness of the wheat in the diets. When diets were fed to broiler chickens either as mash or after pelleting, extent of grinding had no conclusive effect on performance. Pelleting increased performance, and increased apparent metabolisable energy (AME) of the diets from 11.6 to 11.8 MJ/kg. The increase in AME was however, not reflected in a higher starch digestibility. The results indicate that pelleting will even out differences in particle distribution, and that coarse grinding of wheat has no negative effect on broiler performance.