Non-starch polysaccharide degrading enzymes in poultry diets: influence of ingredients on the selection of activities

The use of non-starch polysaccharide (NSP) degrading enzymes as feed additives has consolidated around their application to barley- and wheat-based diets for broiler chicks. Only with this application has a good understanding of their mode of action been developed and reasons for their effectiveness established. Most of the effect of NSP degrading enzymes can be ascribed to reversing the increase in digesta viscosity caused by polysaccharides leached from grain cell walls. Because digesta viscosity is greatest in the youngest birds and decreases with age, the value of supplementary enzymes for older birds is limited to secondary and less well defined effects. These include the release of nutrients otherwise entrapped in the cellular matrix of the feed. Maize alone amongst the commonly used cereals does not appear to release soluble NSPs in amounts sufficient to produce a detectable depression in performance. However, maize is not a homogeneous commodity and for some samples this may not be the case. Use of NSP degrading enzymes with legume seeds can improve nitrogen retention but effects are generally small. The structures of the soyabean NSPs, particularly the pectic polysaccharides, appear unique and existing commercial formulations are not recognised to contain enzymes capable of their degradation. With the present knowledge of soyabean polysaccharide structure, more informed formulation of enzyme products for use with soyabean should enable better responses to be achieved. When coupled with the lesser response from maize, this could allow the effective use of enzyme additives with maize-soyabean diets.