Thesis

Soybean hulls and okara are major by-products of soy processing and have potential as animal feed ingredients; however, their utilization is limited by high fiber content and anti-nutritional factors. Solid-state fermentation has been widely applied to improve the nutritional value of agricultural by-products. This study employed Ganoderma tsugae to ferment a soybean hulls-okara mixture （SOM） to determine the optimal fermentation conditions and evaluate its effects on growth performance, antioxidant status, intestinal health, and gut microbiota in broiler chickens. The results showed that a 6:4 soybean hulls-to-okara ratio fermented for 11 days achieved the optimal fermentation outcome. Fermentation significantly reduced phytate, neutral detergent fiber, and soybean allergenic proteins while increasing total phenolic content and antioxidant activity （p < 0.05）. A total of 450 one-day-old Arbor Acres broilers were assigned to a control diet, diets containing 5% or 10% unfermented SOM （USOM）, or diets containing 5% or 10% fermented SOM （FSOM） for 35 days. Broilers fed 5% FSOM showed growth performance comparable to the control group, while both 5% and 10% FSOM significantly improved feed conversion ratio （p < 0.05）. Moreover, FSOM increased the villus height-to-crypt depth ratio and goblet cell numbers in the jejunum and ileum, reduced ileal Escherichia coli counts, and enhanced jejunal antioxidant enzyme activities. FSOM also downregulated the expression of pro-inflammatory cytokines （IL-1β and IL-6）, whereas USOM suppressed the expression of the intestinal barrier-related gene Claudin-1 （p < 0.05）. In addition, 5% USOM reduced the relative abundance of Firmicutes and increased Proteobacteria in the ileum, while the microbial composition of the 5% FSOM group remained similar to that of the control group. In conclusion, fermenting a soybean hulls–okara mixture at a 6:4 ratio with G. tsugae for 11 days effectively reduced anti-nutritional factors and enhanced its functional properties. Dietary supplementation with 5% FSOM improved intestinal health, antioxidant capacity, and microbial balance without compromising growth performance, indicating its potential as a functional feed ingredient for broiler’s diet.

Keywords: Ganoderma tsugae, Soybean hulls, Okara, Solid-state fermentation, Functional feed