Justifying phytogenic feed additive matrix values in conjunction with exogenous feed enzymes

Phytogenic feed additives (PFA) are purported to possess antimicrobial properties as well as nutrient-sparing characteristics that may aid in alleviating high diet costs. However, for PFA to assist nutritionists, matrix values must be determined and implemented in practical diet formulation. In experiment 1, we used broiler performance measures to evaluate proposed matrix values (PMV) for a commercially available PFA, and we assessed nutrient sparing when the product was combined with a commercial phytase, carbohydrase, and protease that can be described as an exogenous enzyme blend (EEB). In experiment 2, we determined the TME<inf>n</inf> and true amino acid digestibility (TAAD) of the diets used in experiment 1. Main effects and interactions of PFA, PMV, and EEB were determined. Decreasing the basal diet by the PMV of the PFA decreased broiler BW gain and increased FCR. Including PFA in this diet restored BW gain and FCR. The PFA was not additive or synergistic with EEB. Incorporating PFA with PMV and EEB tended to decrease the TME<inf>n</inf> and tested the TAAD. Decreased 4- to 21-d broiler BW gain, TME<inf>n</inf>, and TAAD associated with using PFA with PMV and EEB may be associated with several mechanisms regarding plane of nutrition, gut microflora, substrate competition, or their combination.