Biochemical characteristics of wheat and their relation with apparent metabolisable energy value in broilers with or without non-starch polysaccharide enzyme

Exogenous non-starch polysaccharide (NSP) enzymes do not always exhibit the same improvement in AMEn (apparent metabolisable energy corrected for nitrogen balance) in wheat-fed broiler chickens. In order to understand the factors that determine this variation, the in vitro mode of action of an NSP enzyme preparation (Rovabio Excel) was investigated in several wheats and wheat extracts. In vivo experiments were also performed in broilers fed seven different wheat cultivars. In vitro studies showed an important solubilisation of insoluble arabinoxylan (AX) in wheat flours, ranging from 65 to 85% depending on the wheat cultivar. The negative correlation observed between arabinose/xylose ratio and AX solubilisation (r² = 0.45, P = 0.001) suggests that the variation in solubilisation can be partly explained by the AX structure. NSP enzymes are also able to hydrolyse wheat bran AX by 30-50% depending on the enzyme dosage. Whereas rapid solubilisation of insoluble AX was confirmed in pig digestive physiological conditions (TIM-1), only a minor proportion of AX was hydrolysed as <8 kDa oligomers and then absorbed. In vivo studies on wheat-based diets showed an average AMEn improvement of 108 kcal kg⁻¹ dry matter (DM) (P < 0.001), but a large variation in enzyme efficacy (up to 200 kcal kg⁻¹ DM) was observed. Among the wheat characteristics measured, only a significant negative correlation between AMEn improvement and wheat moisture content was found (r² = 0.71, P = 0.035). A tendency of positive correlation between AMEn improvement with Rovabio Excel and the arabinose/xylose ratio of water-soluble AXs of wheat (r² = 0.42, P = 0.068) and between the arabinose/xylose ratio of water-soluble AXs and the moisture content of wheat (r² = 0.52, P = 0.064) was also observed. It can be deduced from the results that the AX structure might influence the efficiency of enzyme supplementation. In feed, Rovabio Excel quickly solubilises the different AXs of various wheat cultivars as a result of its broad enzyme activity profile. However, relationships between wheat characteristics and the response of wheat batches to enzyme addition are not yet fully understood.