Wheat is one of the major feed ingredients in poultry diets in Europe because of its high starch and protein content. Non-starch polysaccharides (NSP) from wheat, however, are known for their anti-nutritional effects in poultry and in addition their concentrations can be very variable. Current feed formulations do not take into account this variability. This article discusses the importance of NSP in broiler nutrition and the possibility of near-infrared reflectance spectroscopy (NIRS) to monitor their concentrations.
By Natasja Smeets and Filip Nuyens, Kemin Europa NV, Belgium
Two main theories explain the antinutritional characters of non-starch polysaccharides (NSP) in wheat. The first is the so-called 'cage effect'. It is believed that NSP in the cell walls impair nutrient availability to the animal by blocking the access of endogenous digestive enzymes to the cell contents. This is related to the insoluble NSP present in the feed. A second theory implies that the soluble NSP increase the viscosity of the intestinal contents, which causes digestive issues. Feed enzymes such as xylanase, -glucanase and cellulase are added to diets to break down the NSP-fraction.
The chemical composition of wheat can be very variable, depending not only on wheat variety but also on growing conditions, storage and weather conditions. As a result of this variability, the apparent metabolisable energy (AME) of the diet can also vary considerably and this has been mainly attributed to the variable NSP content. The range has been reported between 8.49 to 15.9 MJ/kg.
In a current research program at Kemin, more than 120 European wheat samples were collected from 13 European countries over the last three harvest years. All these wheat samples were analysed for their NSPcomposition by a chemical method. After degradation of starch with -amylase and amyloglucosidase, the obtained residues were filtered, separating the liquid filtrate (soluble NSP) and the solid residue (insoluble NSP). The residues were hydrolysed with sulphuric acid and the released monosaccharides were transformed into alditol acetates by borohydride reduction and treatment with acetic anhydride in the presence of 1-methylimidazol. Quantification of the alditol acetates was performed using gas liquid chromatography with flame ionisation detection. Soluble and insoluble NSP were then calculated as the sum of the monosaccharides arabinose, xylose, mannose, galactose and glucose in the corresponding fractions.
The wide variation in soluble and insoluble NSP is shown in Figure 1. Soluble NSP ranged between 0.83% and 1.83% dry matter (dm), while the concentration of insoluble NSP was between 6.25% and 9.61% dm. As NSP are known to be responsible for a variable AME content of the diets, this variation could have a major impact on animal performance.
Susceptibility of wheat NSP to enzyme hydrolysis
It has also been stated that the effect of adding NSP-degrading feed enzymes is the largest for batches of cereals with low nutritional value, which tend to have high levels of NSP. Degradation of NSP by the use of enzymes in the feed reduces the variation in animal performance due to wheat quality. Since the measurement of NSP in wheat by traditional chemical methods is too time-consuming for routine feed production, it is not obvious to match enzyme application with actual wheat quality and to completely eliminate variability in animal performance.
To test this theory, an in vitro NSP-degradation model was used to assess the effect of adding a single xylanase to different wheat samples with varying compositions. Five different wheat varieties were chosen based on their NSP composition. The enzyme used was the xylanase component of Kemzyme®. After treatment of the wheat samples with amylase and amyloglucosidase, xylanase was added and the samples were incubated at 40°C for 4 hours. After this, the samples were centrifuged to separate the soluble and insoluble NSP and the monosaccharides in the fractions that were quantified as described before. Degradation of NSP was expressed as the reduction in NSP compared to a control treatment without xylanase (Figure 2). Degradation of soluble NSP was between 15% and 37%, while the degradation of insoluble NSP was between 17% and 21%. These results demonstrate that the effect of the enzyme treatment is dependent on the wheat sample used.
NIRS as a quick measurement of NSP
As the NSP content of the wheat is a very important parameter for its nutritional quality, it would be useful to have a quick measurement available for these NSP. In a contrast to chemical NSP-analyses, which are very time consuming, NIRS is a very rapid analytical technique that is already widely implemented in the feed industry for the measurement of feed quality parameters, such as energy and protein content. In the current research program the variability of NSP content and NSP composition in European wheat is monitored based on chemical methods. The results from these chemical analyses, however also allow the development of calibration equations for a NIRS model that can be used for a quick measurement of NSP in wheat.
A first set of NIRS calibrations for NSP were developed. All wheat samples were scanned with a Buchi NIRFlex N- 500 system and the combined spectra and chemical data were subjected to chemometric analysis over the standard NIR wavelength range (1100-2500 nm). The correlation coefficient (r) for total NSP in whole wheat was 0.80. The correlation coefficients for soluble and insoluble NSP in ground wheat were 0.74 and 0.80, respectively. The standard errors of the NIRS calibration were relatively low compared to the high natural variability in wheat NSP, hence supporting the feasibility of the measurement of wheat NSP by NIRS.
Future potential for the feed industry
The purpose of this project is to track the natural variability in NSP content and to develop a fast, convenient and cost effective way to apply systems to monitor these NSP's in wheat. The study has shown that the prediction of NSP in wheat by use of NIRS is feasible. The measurement of NSP in wheat by NIRS will allow the use of enzymes in feed that are adjusted to the actual NSP characteristics of the wheat. A quick and robust method for the determination of NSP in wheat also allows feed mills to purchase wheat that conforms to certain NSP specifications. As prices of raw materials increase further and feed is still about 70% of the total cost of broiler production, managing NSP in feed is a key element to optimise feed costs while maintaining animal performance. The application of enzymes will play an essential role in this concept.
[Source: Enzyme special]