Influence of Inclusion Level of Barley in Wheat-Based Diets and Supplementation of Carbohydrase on Growth Performance and Nutrient Utilisation in Broiler Starters

The influence of inclusion level of barley in wheat-based diets and supplementation of a multicomponent non-starch polysaccharide (NSP) degrading enzyme (Ronozyme® Multigrain) on growth performance and nutrient utilisation in broiler starter (d 0 to d 21) was evaluated. The activities of endo-1,4-β-glucanase, endo-1,3(4)-β-glucanase and endo-1,4-β-xylanase in enzyme were 800 BGU/g, 700 BGU/g and 2700 XU/g, respectively. Normal-starch (non-waxy) hulled barley (NSH) was evaluated with five inclusion levels (0, 141, 283, 424 and 565 g/kg, with corresponding wheat inclusion levels of 629, 472, 314, 157, 0 g/kg; as fed basis) and two levels of enzyme supplementation (0 and 150 mg/kg of feed). A 5 × 2 factorial arrangement of 10 treatments was used and all diets were formulated to be equivalent in respect of metabolisable energy and digestible amino acid contents (11.9 MJ/kg AMEn, 12.2 g/kg digestible lysine, 9.6 g/kg Ca, 4.8 g/kg npp). A total of 400, day-old male broiler chicks was allocated to 50 cages (5 cages/treatment; 8 birds/cage). The inclusion level of barley had a significant effect on weight gain (WG; P < 0.01), feed intake (FI; P < 0.001) and feed conversion ratio (FCR; P < 0.001), whereas enzyme effect was significant only for WG (P < 0.05) and FCR (P < 0.001). Regardless of enzyme supplementation, WG showed a gradual increase up to 283 g/kg inclusion of NSH and reduced with NSH inclusion above this point. Inclusion of NSH at 424 and 565 g/kg significantly (P < 0.05) suppressed FI. Increasing levels of NSH, however, resulted in lower (P < 0.05) FCR. Enzyme addition increased WG and improved FCR for each level of barley inclusion. Inclusion level of barley and enzyme supplementation had significant effects on coefficients of apparent ileal digestibility (CAID) of starch, nitrogen and fat (P < 0.001 to 0.05). Birds fed diets with highest inclusion of wheat or barley showed the lowest and highest CAID, respectively, for all three parameters measured. Digestibility of all parameters was improved by enzyme inclusion (P < 0.05) regardless of barley inclusion level. Three major modes of action of NSP-degrading enzymes have been recognised in previous studies; (i) reduction of digesta viscosity (Almirall et al., 1995), (ii) release of encapsulated nutrients via cell wall degradation (Bedford, 1996) and, (iii) improved gut microflora through supply of prebiotic oligosaccharides (González-Ortiz et al., 2017). Inclusion level of barley resulted in significant effects on gizzard pH (P < 0.05). Gizzard pH decreased beyond 283 g NSH/kg in the diet corresponding to decreased FI. The current data suggest that, although increasing the inclusion level of NSH up to complete replacement of wheat improved FCR, the best inclusion level of NSH for WG was 283 g/kg of diet. Increasing NSH inclusion improved nutrient utilisation possibly through better gizzard function through better function of gizzard. FCR and nutrient digestibility can benefit from carbohydrase supplementation of wheat- and barley-based diets, irrespective of their inclusion level.