Effects of partial soybean meal replacement with sunflower meal and non-starch polysaccharide degrading enzymes supplementation on broiler growth performance, nutrient digestibility, and gut morphology

Background and Aim: Soybean meal (SBM) is the primary protein source in broiler diets; however, its high cost and import dependency necessitate alternative protein sources. Sunflower meal (SFM) is a viable alternative but contains high fiber and non-starch polysaccharides (NSPs), which can impair nutrient utilization. This study evaluated the effects of partially replacing SBM with SFM, with or without NSP degrading enzymes (NSPase) enzyme supplementation, on growth performance, nutrient digestibility, digesta viscosity, and gut morphology in broilers. Materials and Methods: A total of 588 day-old Ross-308 broiler chicks were randomly assigned to six dietary treatments following a 3 × 2 factorial design, with three levels of SBM replacement (0%, 10%, and 20% SFM) and two levels of NSPase supplementation (0 or 100 g/ton feed). Diets were formulated for the starter (1–10 days), grower (11–21 days), and finisher (22–35 days) phases. Growth performance (body weight gain [BWG], feed intake [FI], feed conversion ratio [FCR]), nutrient digestibility (dry matter, crude protein, ether extract, and crude fiber [CF]), digesta viscosity, and gut morphology (villus height [VH], crypt depth [CD], villus width, and villus-to-crypt ratio) were assessed. Statistical analysis was conducted using two-way analysis of variance with Tukey’s test for mean comparisons (p < 0.05). Results: Replacing SBM with up to 20% SFM did not significantly impact BWG (p > 0.05), FI (p > 0.05), or FCR (p > 0.05). However, digesta viscosity increased significantly with higher SFM levels (p < 0.001), while NSPase supplementation reduced viscosity (p < 0.001). CF digestibility was lower with increasing SFM levels (p < 0.01) but improved with NSPase addition (p < 0.01). Gut morphology parameters, including VH and CD, were negatively affected by higher SFM inclusion but showed improvement with NSPase supplementation. Conclusion: SBM can be partially replaced with up to 20% SFM in broiler diets without compromising growth performance. However, increasing SFM levels can reduce CF digestibility and increase digesta viscosity. The addition of NSPase enzymes mitigates these adverse effects by enhancing fiber digestibility and reducing gut viscosity. These findings support the use of SFM as an economically viable protein alternative in broiler feed formulations, particularly in SBM-importing regions.