Nutritional evaluation of two barley cultivars, without and with carbohydrase supplementation, for broilers: metabolisable energy and standardised amino acid digestibility.

1. Two experiments were conducted to assess the nitrogen-corrected apparent metabolisable energy (AMEn; Exp. 1; 288 Ross 308 male broilers at d 14; 36 cages with eight birds each) and coefficient of standardised ileal digestibility (CSID) of amino acids (AA; Exp. 2; 336 Ross 308 male broilers at d 21; 42 cages with eight birds each) of two barley cultivars for broilers in comparison to wheat, without or with a multi-component non-starch polysaccharide (NSP) degrading enzyme. A 3 × 2 factorial arrangement of treatments was used in both experiments with three types of grains (normal starch hulled barley [NSH], waxy starch hull-less barley [WSHL], and wheat) and two levels of enzyme supplementation (0 and 200 g/tonne of feed). Enzyme supplemented diets contained 406 and 128 of endo-1, 4-β-xylanase and endo-1, 3 (4)-β-glucanase units per kg of feed, respectively. 2. Analysis showed that the starch content was higher in NSH (610 g/kg) than in wheat (537 g/kg) and WSHL (554 g/kg), and the composition of starch differed markedly among the grain types. The β-glucan content was considerably higher in WSHL (68.6 g/kg) compared to NSH (38.5 g/kg) and wheat (7.74 g/kg). The contribution of soluble fraction to the total non-starch polysaccharides was higher in WSHL (38.2%) compared to NSH and wheat (17.1% and 13.3%, respectively). 3. A significant (P < 0.01) interaction was observed between the grain type and enzyme supplementation for AMEn. The WSHL, with the highest content of β-glucan, showed the greatest response to enzyme supplementation for AMEn. 4. Birds fed wheat- and WSHL-based diets had the highest and lowest CSID of nitrogen and most of AA, respectively, with NSH diets being intermediate. Regardless of grain type, enzyme supplementation increased (P < 0.05) the CSID of nitrogen. 5. These data suggest that β-glucan content plays an important role in determining the digestibility of nutrients in barley for broilers, resulting in a better feeding value for NSH over WSHL. Supplementation of a multi-component NSP-degrading enzyme can improve the feeding value of barley in broiler diets by increasing the digestibility with the effect being more pronounced in WSHL barley.