Scaling-up fungal pretreatment of lignocellulose biomass: Impact on nutritional value, ruminal degradability, methane production, and performance of lactating dairy cows

Scaling-up fungal pretreatment of lignocellulose biomass (LCB) for ruminant nutrition has become a major research challenge in recent years. This study systematically investigated the effectiveness of fungal (Pleurotus ostreatus) pretreatment (for 30 days under solid state fermentation (SSF)) of large quantities (8400 kg) of lime-pasteurized wheat straw, in terms of improvement in nutritional value, in vitro ruminal fermentation characteristics and methane (CH₄) production potential. We further investigated the effects of stepwise replacement of untreated wheat straw (UTWS) with the lime pasteurized P. ostreatus treated wheat straw (PTWS) on dry matter intake (DMI), apparent total tract digestibility, production performance, CH₄ emission and feed efficiency of lactating dairy cows. The results revealed that PTWS had lower lignin (P < 0.001), hemicellulose (P < 0.001) and cellulose (P < 0.05) contents and higher crude protein (CP; P < 0.001) content and cellulose to lignin ratio (P < 0.01), as compared to UTWS. The PTWS had higher in vitro DM digestibility (IVDMD; P < 0.001), total gas production (IVGP; P < 0.01), total volatile fatty acids (VFAs, P < 0.01) and propionate (P < 0.05) concentration, and lower (P < 0.05) pH and CH₄ gas production during 72 h in vitro fermentation. Notably, the fungus degraded 33.3 % lignin at the expense of 6.56 % cellulose, and markedly increased CP content (46.3 %), IVDMD (20.2 %), IVGP (16.8 %) and VFAs (10.0 %) production, and decreased CH₄ production (10.3 %). The aflatoxin B₁ concentration of PTWS was <5.0 µg/kg, and mycelium concentration was 181.9 mg/kg DM, reflecting safe and effective tretment of the straw. Replacement of 32 % UTWS in total mixed ration with the PTWS, increased DMI (0.84 kg/day; P = 0.01), apparent total tract DM digestibility (5.5 g/100 g; P < 0.05) and milk yield (1.17 liter/day; P = 0.032), and decreased CH₄ emission (1.45 g/kg DMI; P < 0.05). In conclusion, hydrated lime can replace traditional high-tech pasteurization methods for the fungal pretreatment of LCB, and present prospects for scaling up the process for ruminant nutrition.