Wheat straw is an abundant but low-quality lignocellulosic resource. This study investigated the bioconversion of wheat straw using cellulolytic fungi to increase cell wall digestibility. Twenty-five native Trichoderma isolates were screened, and the three most active strains—FUM20, FUM28, and FUM6—were studied for their bioconversion characteristics. Among these, FUM20 (Trichoderma longibrachiatum) demonstrated superior performance, exhibiting a five-fold higher filter paper cellulase (FPase) activity (P = 7.7E-8), and a three-fold increase in extracellular protein secretion compared to the reference strain Trichoderma reesei QM6a (P = 6.1E-8). Optimal enzyme activity for all isolates was observed at 50 °C and pH 4.8. A 60% greater dry matter loss was found when wheat straw was cultured in solid-state fermentation with FUM20 in vitro compared to untreated wheat straw (P = 3.6E-4). In situ rumen incubation revealed that FUM20 pretreatment significantly enhanced dry matter digestibility by 25% (P = 4.7E-5) and neutral detergent fiber (NDF) digestibility by 40% (P = 3.7E-5). Our findings identify FUM20 as a highly promising candidate for the biotechnological valorization of wheat straw, leveraging its high secretory capacity for cellulase-rich enzymes to improve feed quality and support sustainable livestock production.

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