Effects of Mixed-Strain Solid-State Fermentation on Mycotoxin Levels and Feeding Value of a Mixture Containing Spent Flammulina velutipes Substrate for Yellow-Feathered Broilers

Spent Flammulina velutipes substrate (SFVS) is nutritious, but its high crude fiber content and contamination with zearalenone (ZEN) and deoxynivalenol (DON) may limit feed use. This study optimized mixed-strain solid-state fermentation (SSF) of an SFVS-containing mixture and evaluated feeding value using 420 one-day-old male yellow-feathered broilers. Optimal conditions were a 2:1:2:3 inoculum ratio of Saccharomyces cerevisiae, Bacillus coagulans, Clostridium butyricum, and Bacillus subtilis, with 5-day fermentation, 47% moisture, and 7% inoculum. In the mixture, ZEN and DON concentrations decreased from 8622.43 and 1612.74 to 1349.82 and 750.21 μg/kg (84.35% and 53.48% reductions). Fermentation increased crude protein and total measured amino acids, decreased crude fiber (p < 0.01), and increased in vitro digestibilities of dry matter, crude protein, and crude fiber (p < 0.05). Over 42 d, 3% and 5% inclusion of the fermented mixture increased body weight (BW) on days 21 and 42 and average daily gain (ADG), while reducing feed conversion ratio (FCR) versus unfermented-mixture treatments (p < 0.05). At 3% and 5% inclusion, serum antioxidant status and jejunal morphology improved, while breast meat cooking loss and overall texture were not adversely affected; cecal communities were generally closer to the control (CON). The 7% inclusion provided no further benefit.