Mechanism of action and potential environmental benefits from the use of feed enzymes

Abstract

The efficiency of utilisation of wheat, oats, barley and rye by poultry is often limited by the presence of antinutritional factors (ANFs). Such ANFs are commonly referred to as non-starch polysaccharides, classified as arabinoxylans and β-glucans. The arabinoxylans, which consist of a linear backbone of xylose substituted with arabinose, are responsible for the bulk of the problems encountered in birds fed wheat or rye based diets, whilst the β-glucans, a linear polymer of glucose with kinks in its structure, are responsible in oats and barley. However it is only the high molecular weight arabinoxylans and β-glucans that are responsible. Both β-glucans and arabinoxylans exert their negative effects on digestion by creation of very large entanglements which result in an elevation of viscosity of the small intestine. Such an elevation results in a reduction in the rate of digestion and absorption of nutrients, an elevation of microbial activity in the intestine, a reduction in feed intake and increased litter moisture. The application of relevant and effect xylanases and β-glucanases can alleviate these problems by reducing the molecular size of the target substrate, which in turn reduces the viscosity of the intestine and hence enables more rapid digestion. It is unlikely that exogenous enzymes reduce the β-glucans and arabinoxylans to their constituent sugars since relatively few catalytic events are necessary to reduce the molecular size and hence viscosity of these complexes. A more detailed understanding of the structure of these viscous complexes as they appear in the intestine will enable the design of more specific enzymes for poultry feeds.