Solid-state fermentation with white-rot fungi is an interesting alternative to chemical straw treatment for ruminant nutrition. However, for practical implementation on farms, feasible handling and its effect on nutritional characteristics have to be tested beforehand. Chopped wheat straw was either soaked and drained or just remoistened to about 24% dry matter without subsequent sterilization. Moist straw was inoculated with Pleurotus ostreatus, Ceriporiopsis subvermispora, or Volvariella volvacea. Fermentation lasted up to 42 d with weekly or shorter sampling intervals. Fiber fractions, minerals and elements, and non-starch polysaccharides were analyzed, and microflora was plate counted. Lactic acid bacteria of selected samples were identified by MALDI-TOF. All inoculated fungi grew well under the selected conditions expressed by the visible mycelium and specific smell. P. ostreatus developed fruiting bodies in the given time. Initial numbers of lactic acid bacteria were >8.0 log cfu/g. In the beginning, Weissella confusa/cibaria dominated. However, neither decrease in lignin nor cellulose concentration was observed during the period in either of the treatments, thus seeming to be inappropriate for ruminant nutrition purposes. Some elements and minerals peaked, especially towards the second and third week (Na, Cl, Mg, Fe, and Mn). Growth conditions for mushrooms were optimized by remoistening the straw with a defined amount of water.

Biological treatment of cereal straw for ruminant nutrition purposes might present an environmentally friendly option of valorizing a widely available by-product of grain production for farming systems with low external input. Several strains of white-rot fungi have been selected in the past under mostly controlled laboratory conditions for their capacity of lignin degradation. The study adapted to conditions on farm for upscaling purposes. The development of the in vitro straw digestibility with two different moistening pre-treatments and inoculated with three different fungi species, namely Pleurotus ostreatus, Ceriporiopsis subvermispora and Volvariella volvacea, was determined up to 42 days of fermentation with five sampling times. The effect of physical straw pre-treatments on nutritional parameters was evaluated. The neutral detergent fiber digestibility (NDFD30h), enzymatically soluble organic substance (ELOS) and the gas production (Hohenheim Feed value Test, HFT) as indicators for in vitro ruminal degradability decreased over time independent of the fungus: HFT, ELOS and NDFD30h by up to 50, 35 and 30% of the original straw. Remoistening and autoclaving the straw increased the gas production significantly by 2.6 mL/200 g dry matter (DM), and ELOS and NDFD30h by 45 and 51 g/kg DM compared to the original straw (34.9 mL/200 mg DM, 342 g/kg DM, 313 g/kg NDF).

Weather extremes in parts of Europe have led to a renewed search for alternative feeds for ruminants. Cereal straw presents one source of fibre, which is hard to digest due to its lignin-carbohydrate complexes. Chemical and biological treatments have been investigated to improve digestibility. Here, the applicability of alkaline treatments for farming conditions under EU legislation and their efficacy were checked. Thus, we tested caustic soda (60, 120 g kg-1straw) and urea (15, 30, 45, 60 g kg-1 straw without and with urease addition) applications both at laboratory scale and using a mixer-wagon. The nutritive value was evaluated analyzing chemical parameters including fibre components and estimating in vitro digestibility. The in vitro digestibility indicated by gas production, enzymatically soluble substrate and neutral detergent fibre digestibility (30h) was highest for the NaOH treatments, which did not differ by dose. Remoistening the straw to 600 g DM kg-1 was a precondition for the effectiveness of both treatments. Urease addition enhanced the intended ammonification when urea was applied at ≥ 30 g kg-1. An ambient temperature for urea treatment ≥ 25 °C was necessary and had to be maintained for at least 14 d post treatment. The determination of crude ash in NaOH treated feeds by the standard procedure and time overestimated the mineral fraction and had to be modified. This systematic approach provides guidance for feasible straw treatments for EU farmers. However, trials for feed acceptance and in vivo digestibility are needed to demonstrate the real effect in animals.