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The purpose of this study was to determine how ruminal Crabtree-negative yeast affects the nutritional characteristics of winged bean (<i>Psophocarpus tetragonolobus</i>) tubers (WBT), in vitro gas and digestibility, and rumen fermentation. The experiment was carried out in a randomized complete design with a 5 × 2 (+1) factorial arrangement. Factor A determined the WBT products (a₁ = dry WBT, a₂ = fermented WBT without yeast in media solution, a₃ = fermented WBT with <i>Pichia kudriavzevii</i> KKU20, a₄ = fermented WBT with <i>Candida tropicalis</i> KKU20, and a₅ = fermented WBT with <i>Saccharomyces cerevisiae</i>), whereas factor B determined the level of fermented WBT replacing cassava chips (b₁ = WBT at 50% and b₂ = 100% levels). The results of the experiment showed that the fermentation approach could increase the crude protein (CP) content of WBT by around 7% (<i>p</i> < 0.01). The WBT fermented with yeast lowered the number of aerobic bacteria during the fermentation process (<i>p</i> < 0.01). <i>P. kudriazevii</i> KKU20 yeast strain had a 17.3% higher final asymptotic gas volume (<i>Vf</i>) than the <i>C. tropicalis</i> KKU20. Crabtree-negative yeast had a higher in vitro dry matter digestibility (IVDMD) than Crabtree-positive yeast after 12 h of incubation (<i>p</i> < 0.01). Fermented WBT with yeast had a higher IVDMD after 24 h of incubation than fermented WBT without yeast in the media solution (<i>p</i> < 0.05). The fermented WBT with <i>C. tropicalis</i> KKU20 enhanced propionic acid (C3) concentrations when cassava chips were replaced for half of all of the diet (C3 ranged from 26.0 to 26.4 mol/100 mol; <i>p</i> < 0.01). Furthermore, Crabtree-negative yeast isolated from the rumen stimulates rumen bacteria more effectively than Crabtree-positive yeast (<i>p</i> < 0.01). According to our findings, nutritional enrichment with yeast might increase the in vitro gas production and digestibility of WBT. The study also demonstrated that Crabtree-negative yeast has a promising lead in terms of improving rumen fermentation quality. However, further research is required before deciding on an effective approach for optimizing the potential of WBT as a feed source.