Enzyme-assisted valorization of agro-industrial byproducts for sustainable and efficient broiler production.

Agro-industrial byproducts, including distillers dried grains with solubles, sunflower seed meal, palm kernel cake, sweet orange peel meal, brewers' dried grain, and various fruit and vegetable processing wastes, represent abundant, low-cost alternatives to conventional feed ingredients such as corn and soybean meal in broiler chicken diets. Their incorporation supports sustainability by reducing feed costs, alleviating food-feed competition, and promoting circular bioeconomy principles through waste valorization. However, the presence of complex non-starch polysaccharides, lignocellulosic structures, phytate, mannans, and other antinutritional factors often limits nutrient digestibility, impairs intestinal health, and compromises broiler growth performance when these byproducts are included at higher levels. Exogenous enzyme supplementation, particularly phytase, protease, xylanase, β-glucanase, β-mannanase, cellulase, and multi-enzyme complexes, has emerged as an effective strategy to overcome these limitations. Enzymes hydrolyze indigestible components, reduce digesta viscosity, improve nutrient availability (dry matter, crude protein, energy, and phosphorus), enhance intestinal morphology (increased villus height to crypt depth ratio), modulate gut microbiota toward beneficial populations such as Lactobacillus and Bifidobacterium, and mitigate inflammatory responses. These improvements enable substantially higher inclusion levels of byproducts, up to 50% substitution of conventional ingredients in some cases, without negative effects on body weight gain, feed conversion ratio, or overall performance. Reported performance gains include 1%-16% increases in weight gain, 2%-11% in feed intake, and 1%-26% reductions in feed conversion ratio, depending on byproduct type, enzyme combination, and inclusion level. Economically, enzyme supplementation often offsets its initial cost through better feed efficiency, resulting in lower production cost per kilogram of broiler meat (reductions of 7%-12% in several studies). Environmentally, the approach decreases reliance on high-carbon-footprint crops, reduces manure emissions, lowers greenhouse gas contributions from feed production, and supports waste minimization. Challenges remain, including variability in byproduct composition, enzyme specificity and stability, seasonal quality fluctuations, and occasional inconsistent results across trials. This review concludes that strategic enzyme supplementation offers a practical, science-based pathway to increase the sustainable and efficient utilization of agro-industrial byproducts in broiler production. Future efforts should focus on tailored multi-enzyme formulations, integration of omics technologies for precise matching of enzymes to specific byproducts, and large-scale commercial validation to facilitate wider industry adoption.