Fungal Pretreatment of Lignocellulosic Feedstocks: Challenges and Opportunities in Lignin Degradation, Structural Polysaccharide Preservation, and Conversion into Ruminant Feed

This review provides a comprehensive meta-summary of recent literature on fungal pretreatment of lignocellulosic biomass (LCB), emphasizing selective lignin degradation and polysaccharide preservation to improve the nutritive value of treated biomass for ruminant nutrition. It explores how white-rot fungal (WRF) species, substrate composition, and incubation duration influence lignin removal, carbohydrate retention, crude protein enrichment, and ruminal fermentability. Selective degraders, such as Ceriporiopsis subvermispora, Lentinula edodes, and Pleurotus eryngii, achieve extensive lignin degradation with minimal carbohydrate loss, markedly improving nutritional quality and fermentation efficiency. A minimum incubation period of 22–30 days optimizes ruminal fermentation by balancing maximal lignin breakdown with minimal carbohydrate loss. Although feeding trials demonstrate promising outcomes, large-scale adoption remains limited by lengthy incubation and pasteurization requirements. This review underscores the importance of achieving selective delignification with minimal nutrient loss and emphasizes the need for standardized, scalable, and time-efficient fungal pretreatment protocols to enhance feed value, advance sustainable livestock production, and support circular bioeconomy goals.