Influence of carbohydrase supplementation on metabolisable energy and ileal nutrient digestibility of two cultivars of barley for broilers

The use of barley in broiler diets is limited because of the presence of β-glucans, which negatively influence nutrient utilisation and bird performance. These negative effects may be partly overcome by exogenous carbohydrases containing β-glucanases. In the current study, the influence of a multi-component carbohydrase (Ronozyme multigrain, DSM Nutritional Products, Singapore) on nitrogen-corrected apparent metabolisable energy (AMEn; assay 1), and, apparent ileal digestibility (AID) of starch and standardised ileal digestibility (SID) of nitrogen (N) and amino acids (AA; assay 2) of two barley cultivars was examined. A 2 × 2 factorial arrangement of treatments was used in both assays with two barley cultivars (normal hulled barley [NB] and waxy hull-less barley [WHB]) and two levels of enzyme supplementation (0 and 200 g/tonne feed). Assay diets contained barley (962 and 917 g/kg in assays 1 and 2, respectively), fortified with mineral and vitamin supplements. Each assay diet was fed to six replicate cages (eight 14-day old male broilers per cage). In assay 1, total excreta collection was carried out from day 17 to 21 post hatch for the determination of AMEn. In assay 2, ileal digesta samples were obtained on day 21 post hatch and apparent digestibility was calculated using the ratio of the inert marker (Titanium dioxide at 5 g/kg) in the diet and digesta. The SID of N and AA were calculated using endogenous losses determined in broilers fed a nitrogen-free diet.

Differences were observed in N and fibre contents of the barley cultivars. The contents of dry matter, N, insoluble and soluble dietary fibre of NB and WHB were: 893 and 907, 101 and 133, 142 and 110, and 29 and 68 respectively. Starch content was higher in NB (610 g/kg) than WHB (554 g/kg), and the composition of starch differed markedly between the cultivars. The amylopectin content of the starch in NB was 343 g/kg, whereas in WHB cultivar the content was 477 g/kg. β-glucan content also differed, with WHB having higher concentration compared to NB (69 and 38 g/kg, respectively). Higher β-glucan content of WHB is in agreement with previous data (Izydorczyk et al., 2000). The main effect of cultivar was significant (P < 0.001) for AMEn, with higher value (12.17 MJ/kg) observed for NB compared to WHB (9.92 MJ/kg). Added enzyme increased (P < 0.001) the AMEn (11.38 vs 10.72 MJ/kg) and AID of starch (0.946 vs 0.911) in both cultivars, but the magnitude of response was greater in WHB resulting in a tendency (P < 0.07 - 0.10) for a cultivar x enzyme interaction. The main effect of cultivar was also significant for the SID of N (P < 0.01) and most AA (P < 0.05- 0.001), with higher values determined for NB. The coefficient of SID of N in NB and WHB were 0.79 and 0.75, respectively. Enzyme addition tended (P = 0.07) to improve N digestibility, but had no effect (P > 0.05) on AA digestibility. The present data indicate that the responses in starch digestibility and AMEn with enzyme addition were greater in WHB than in NB. The poorer nutrient utilisation indices of WHB, however, highlight the need to consider β-glucan content in the selection of barley cultivars for use in broiler diets.