Evaluating the Nutritional Bioefficacy of Xylanase and Cellulase in Poultry Diets Rich in Non-Starch Polysaccharides

The incorporation of agro-industrial by-products into poultry feed offers a sustainable strategy for reducing reliance on conventional grains while diversifying nutritional inputs. However, the high content of non-starch polysaccharides (NSPs), particularly arabinoxylans and cellulose, limits nutrient utilization in monogastric animals due to increased digesta viscosity and structural barriers to nutrient release. Xylanase and cellulase are two widely studied exogenous enzymes that target these polysaccharides, enhancing nutrient accessibility in high-fiber poultry diets. This review aimed to synthesize evidence on the functional roles of xylanase and cellulase in degrading plant cell wall components and improving feed utilization. The present review synthesizes current evidence on the functional mechanisms of xylanase and cellulase in degrading plant cell-wall polysaccharides and enhancing feed utilization, with particular attention to the application of xylanase and cellulase in diets formulated with wheat pollard, rice bran, and other NSP-rich ingredients. Although numerous studies reported improved feed efficiency, digestibility, and growth performance following xylanase and cellulase enzyme supplementation, proximate analyses often indicated minimal or no changes in crude protein, fiber, or fat contents of enzyme-treated diets. The lack of compositional change, hereafter referred to as proximate compositional stability, has received limited attention as a potential indicator of enzymatic bio-efficacy. By integrating biochemical, nutritional, and physiological evidence, the present study highlights the interpretive gap between chemical composition and biological function in feed evaluation. The review further proposes that proximate compositional stability in an enzyme-supplemented diet does not indicate a lack of enzyme activity; rather, it represents a baseline condition confirming enhanced nutrient utilization. Recognizing this distinction is critical to developing function-oriented evaluation frameworks that support the effective use of fibrous by-products in poultry nutrition, aligned with broader goals of sustainable and resource-efficient animal production.