**Background:** Drought conditions in Europe (2018–2020) created a shortage of roughage for ruminants, renewing interest in alternative fiber sources such as cereal straw. Although wheat straw is abundant—over 8 million tonnes of dry matter are recycled annually in Germany alone—its high lignin content and strong lignin-carbohydrate complexes limit digestibility. Biological treatment with white-rot fungi has been proposed as a method to degrade lignin and improve straw digestibility, but practical farm-scale implementation has been lacking. This study aimed to test three fungal strains (Pleurotus ostreatus, Ceriporiopsis subvermispora, and Volvariella volvacea) under conditions that could realistically be applied on farms.
**Methods:** Winter wheat straw harvested in July 2018 in Köllitsch, Germany, was used. Four trials were conducted in 2019. Trial 1 used straw soaked in abundant water for 20–24 hours and drained, then inoculated with C. subvermispora CBS 347.63 or P. ostreatus CBS 411.71 or PO93, incubated at 21°C for up to 42 days. Trials 2 and 3 used straw remoistened to a target DM of 250 g/kg, inoculated with V. volvacea DSM 6190 (Trial 2, 24°C, 28 days) or C. subvermispora and P. ostreatus (Trial 3, 23°C, 14 days). A separate physical treatment trial tested the effects of remoistening vs. soaking+draining, with and without autoclaving (121°C, 20 min). Samples were analyzed for DM, crude ash, aNDFom, ADFom, ADL, ether extract, crude protein, ELOS, gas production (Hohenheim Feed Value Test), and NDFD₃₀ₕ. Statistical analysis used ANOVA with Tukey post-hoc tests and linear regression.
**Key Results:** Physical treatment alone showed that soaking plus draining resulted in average DM losses of 90.6 g/kg DM, while remoistening lost only 3.5 g/kg DM. Remoistening plus autoclaving increased NDFD₃₀ₕ by 17% (from 300 to 342 g/kg NDF) and ELOS by 12% (from 348 to 378 g/kg DM) compared to dry straw. However, draining led to higher ADL content (65.7 vs. 52.9 g/kg DM, p<0.001) and lower NDFD₃₀ₕ (303 vs. 342 g/kg NDF, p=0.009) compared to remoistening. For biological treatments, none of the fungal strains improved in vitro digestibility at any time point. NDFD₃₀ₕ was numerically higher within the first 7 days but did not reach statistical significance and declined thereafter. DM losses in remoistened treatments reached approximately 108 g/kg DM within 14 days. The drained C. subvermispora treatment showed low early losses (29 g/kg DM by day 14) but increased to 241 g/kg DM by day 28. V. volvacea showed near-linear DM losses (y=0.725x−0.642, R²=0.97, p=0.002), reaching 192 g/kg DM at day 28. Lignin concentration increased by up to 42 g ADL/kg DM in some treatments. The interaction of fungal strain and storage duration was significant for NDFD₃₀ₕ (p<0.05), ELOS (p<0.01), and HFT (p<0.001) in drained straw, but in remoistened treatments, digestibility indicators decreased uniformly from the second week onward.
**Clinical Implications:** This study demonstrates that under non-sterile, farm-realistic conditions, the tested white-rot fungi failed to improve wheat straw digestibility for ruminants. The findings challenge the feasibility of on-farm fungal treatment as a practical strategy, given the substantial DM losses (up to 241 g/kg DM) and lack of digestibility improvement. Simple physical treatments—particularly remoistening combined with autoclaving—showed more promise, increasing NDFD₃₀ₕ by 17% and ELOS by 12%. However, autoclaving is impractical at farm scale. The authors suggest that hot water treatment may be a more economical alternative. The study underscores the importance of considering pre-treatment losses, competing microflora, and the need for sterile conditions—factors often overlooked in laboratory studies that report positive results with fungal treatment.