A substrate-based approach to enzyme selection and prediction of associated matrix values in broiler diets

High energy and protein prices and volatility of grain, fat, and oilseed meal markets have resulted in shifts in feed ingredient use and increased application of a wide variety of exogenous enzymes to reduce feed cost. However, the choice of enzyme and subsequent application of matrix values are often done with little regard of the substrate levels in the diets that are being targeted. This discord between feed substrates and the class of enzymes being applied has contributed to inconsistent enzyme responses, and nutritionists taking take a generic and conservative view of enzyme matrix values that do not allow maximum feed cost-savings to be achieved. A basic principle when selecting any exogenous enzyme is that the specific enzyme must be effective at targeting nutrients in the diet that are not completely digested by the broiler’s own endogenous enzymes. For example, it is well known that phytate is not inherently well digested, which provides the basis for phytase enzyme use. However, although phytase effects on energy and amino acid digestibility are significantly influenced by the dietary phytate level, phytate substrate levels are frequently not considered when selecting the optimal phytase dose or assigning corresponding matrix values to the enzyme. In a similar manner, the substrate fractions that determine the energy response from ‘carbohydrase’ enzyme can be divided into five main fractions namely, starch, non-starch polysaccharides (NSP), sugars, protein, and fat. For protease enzymes, effects on amino acid digestibility have been shown to also not be constant, but are dependent on the level of each amino acid in the diet and its inherent digestibility. A better understanding of the substrate levels in the diet and the associated enzyme response is required and will allow for a more accurate selection of the class of enzyme to use and its associated nutrient contribution in formulation.

Key words: Broiler, enzyme, substrate, energy digestibility, amino acid digestibility