The effect of xylanase, amylase and protease on the metabolisable energy of various varieties of maize when precision-fed to broiler chickens

The use of maize meal in poultry diets is ubiquitous around the world although relatively less prevalent in northern Europe. Maize is widely used because of its availability and its reputation for being reasonably stable and consistent in its chemical composition. Furthermore, maize contains very few compounds, and in low concentrations, which have antinutrient or non-nutrient properties. Since the major component in maize is starch it is likely that variation in starch structure and composition may cause variation in nutritional value but there are also relatively small amounts of other carbohydrates present, including non-starch polysaccharides (NSP) which total about 100 g/kg (Bach-Knudsen, 2001). The carbohydrate fraction may influence the nutritional value of maize but may be susceptible to treatment by supplemental enzymes. However, enzyme supplementation does not always have a beneficial effect on nutritional value and this may be due to varying susceptibility of maize and its constituent carbohydrates to enzymatic degradation. The purpose of this study was to investigate the efficacy of enzymes from Trichoderma reesei, Bacillus subtilis and Bacillus amyloliquifaciens containing xylanase, protease and amylase activity (Avizyme 1502) on different varieties of maize obtained from Poland. A total of 120 male Ross broilers (about 2 5 kg body weight) were reared on a standard commercial broiler ration and used in a 6 2 factorial study, conducted in a randomised block design. At about 49 d the birds were placed in cages, and after a 48-h period of starvation where a glucose solution was administered by gavage, the birds were precision-fed (50 g) one of the ground maize samples with or without enzyme (0 5 g/kg). Excreta were quantitatively collected over a 48-h period immediately after administration of the samples, dried, weighed, ground and gross energy determined. The apparent metabolisable energy (AME) and the dry matter digestibility coefficients were calculated. Statistical analysis was done using JMP (SAS Institute) as a 2 6 factorial. The starch, oil, protein and dry matter (DM) content of the maize samples were predicted by NIRS. The RSD60 (in vitro starch digestibility) was determined based on the method of Englyst et al. (1992). Protein solubility was determined in vitro in a buffer containing K2HPO4, KH2PO4 and NaCl and is an indicator of the degree of protein and starch interaction (for example, Maillardtype reaction products). The mean AME value for all samples without enzyme was 13 6 MJ/kg DM (Table 1) and this tended to be improved (P < 0 07) with supplemental enzyme by around 0 3 MJ/kg DM. The apparent dry matter digestibility coefficient for the unsupplemented maize was 0 70 but there was no effect of supplemental enzymes. There was no maize enzyme interaction for dry matter digestibility or AME. Supplementation of maize with enzyme tended to improve AME in precision-fed birds. The variability in response may be due to variation in the structure of the maize starch as well as variation in the other component carbohydrates in the different varieties of maize. The one sample of maize (Najdek) that tended to respond negatively to enzyme addition had the highest solubility of protein (Table 2). Interestingly, the improvements in the AME of maize with enzyme are not associated with a concomitant improvement in dry matter digestibility coefficient suggesting a more efficient use of the energy, perhaps linked to a reduction in endogenous losses. It can be concluded that the energy value of maize may be improved with supplemental enzymes though the magnitude of these effects depend on the chemical composition of the maize, perhaps associated with the concentration and susceptibility of carbohydrateand protein-based substrates.