Influence of feed form on the standardised ileal amino acid digestibility of common grains for broiler chickens

The present experiment was carried out to determine the influence of feed form (FF) on the apparent ileal digestibility coefficients (AIDC) of dry matter (DM), starch and, standardised ileal digestibility coefficients (SIDC) of nitrogen (N) and amino acids (AA) in different grain types (GT). Eight experimental diets were developed in a 4 × 2 factorial arrangement of treatments that included four GT (maize, sorghum, wheat and barley) and two FF (mash vs. pellet). A N-free diet was also used to determine the endogenous N and AA losses for the calculation of SIDC values. Titanium dioxide was incorporated in all diets as an indigestible marker. Ileal nutrient digestibility was determined using the direct method. The four assay diets were formulated to contain 938 g/kg grain as the sole source of AA and starch in the diet. The assay diets and N-free diet were randomly allotted to six replicate cages (eight birds per cage) and fed from 19 to 23 d post-hatch and the ileal digesta was collected on d 23. Pelleting reduced (P < 0.05) the AIDC of DM in all test grains. A significant (P < 0.001) GT × FF interaction was observed for AIDC of starch. Starch digestibility was unaffected by FF in maize- and sorghum-based diets but was reduced in pelleted wheat- and barley-based diets. The GT had a significant (P < 0.05 to 0.001) effect on the SIDC of N and AA. In general, the average values for SIDC of AA were higher in maize followed by sorghum or wheat and barley. The FF showed no significant (P> 0.05) effect on the SIDC of N and AA except cysteine and proline, in which the SIDC values were higher (P < 0.05) in mash than the pelleted diets. Overall, the present data suggest that the physical form of the feed can impact the digestibility of DM, starch and AA in broilers. Because the FF effect on nutrient digestibility can vary depending on the grain type and nutrient, the FF effect should be taken into account in feed evaluation assays to achieve the optimum use of nutrients especially AA.