BACKGROUND
This study addressed the underuse of spent mushroom substrate (SMS) as a livestock feed resource. The authors focused on SMS from *Flammulina velutipes* and *Pleurotus eryngii*, noting that edible fungi production in China reached approximately 39.34 million tons in 2019 and that 1 kg of edible fungi typically produces 5 kg of SMS, implying about 197 million tons of fresh SMS in China in 2019. Because SMS generally contains 50% to 75% moisture, storage is difficult, making ensiling a potentially valuable preservation strategy. The investigators hypothesized that lactic acid bacteria and cellulase, especially in combination, could improve fermentation quality, in vitro digestibility, and aerobic stability. They also highlighted baseline differences between the two substrates: before ensiling, the dry matter content of *P. eryngii* SMS was 12 g kg^−1 FW greater than that of *F. velutipes* SMS, water-soluble carbohydrate was 1.4 times higher, and the buffering capacity of *F. velutipes* SMS was 1.8 times higher. Epiphytic lactic acid bacteria counts before ensiling were 4.68 log10 CFUs g^−1 FW for *F. velutipes* SMS and 4.30 log10 CFUs g^−1 FW for *P. eryngii* SMS.
METHODS
This was an experimental laboratory study rather than a clinical trial. Fresh SMS was assigned to 4 treatments: no additive (control), lactic acid bacteria alone (L), cellulase alone (E), or both together (M). *Lactobacillus plantarum* LP1 was applied at 50 mg kg^−1 FW, with an actual count of 4.7 × 10^7 CFUs g^−1 FW. Cellulase from *Trichoderma viride* and *Acremonium cellulolyticus* Y-94 was also applied at 50 mg kg^−1 FW, with actual enzymatic activity of 4.2 × 10^−3 U g^−1 FW. Material was packed into 5 L polyethylene buckets, 5 drums per treatment. Packing density was 550.1 ± 10.0 kg/m^3 FW for *F. velutipes* SMS and 575.0 ± 9.2 kg/m^3 FW for *P. eryngii* SMS. Silage was stored at 21–25 °C for 45 days. Five replicates per treatment were used for in vitro digestibility analyses; 3 replicates were used for fermentation quality analysis, and remaining replicates were mixed for aerobic stability testing. Aerobic stability was defined as the time until silage temperature rose 2 °C above ambient temperature during exposure at 23.5 °C ± 1 °C for 14 days, with temperatures recorded every 6 h. In vitro digestibility testing used 0.5 g samples in ANKOM F57 bags, incubated with rumen fluid from 4 sheep at 39 °C for 72 h. Statistical analyses used independent-sample t-tests, one-way ANOVA with Tukey multiple comparisons, and two-way ANOVA for main effects and interactions.
KEY RESULTS
After 45 days of ensiling, pH in both *F. velutipes* silage and *P. eryngii* silage was lower in the L, E, and M groups than in the control group (p < 0.05). Across silage types, pH, acetic acid, and propionic acid were lower in *P. eryngii* silage than in *F. velutipes* silage (p = 0.000–0.041), while lactic acid was higher in *P. eryngii* silage (p = 0.000–0.020). For *P. eryngii* silage, the pH of the L, E, and M groups was 3.93–3.96, which the authors interpreted as good fermentation. In contrast, *F. velutipes* silage showed lower fermentation quality, with pH 4.2–4.4 and butyric acid 5.0 g kg^−1 DM–11.2 g kg^−1 DM. The mixed treatment also reduced the ammonia nitrogen/total nitrogen ratio in *F. velutipes* silage compared with control (p < 0.05), while the L treatment reduced ammonia nitrogen/total nitrogen in *P. eryngii* silage (p < 0.05). In the discussion, the authors stated that in *P. eryngii* silage, the mixed treatment increased lactic acid by 3.3–6.8% and decreased pH by 0.02–0.28 units compared with the control and the single-additive treatments.
For chemical composition, *F. velutipes* silage had lower dry matter, acid detergent fibre, and acid detergent lignin than *P. eryngii* silage (p = 0.000–0.040), while crude protein was higher (p = 0.001–0.009). In *P. eryngii* silage, dry matter in the L, E, and M groups was higher than control (p < 0.05). Acid detergent fibre was lower with L than control (p < 0.05). Crude protein and neutral detergent fibre were higher in the M group than control (p < 0.05). Acid detergent lignin was lower with E and M than control (p < 0.05).
For energy and digestibility, digestible energy, metabolizable energy, net energy for maintenance, net energy for lactation, and net energy for gain were all higher in *F. velutipes* silage than in *P. eryngii* silage (p = 0.000–0.011). In vitro dry matter digestibility, in vitro acid detergent fibre digestibility, and in vitro neutral detergent fibre digestibility were also higher in *F. velutipes* silage (p = 0.000–0.017). Compared with control, E and M increased in vitro neutral detergent fibre digestibility and in vitro acid detergent fibre digestibility in *F. velutipes* silage (p < 0.05). The E treatment increased in vitro neutral detergent fibre digestibility and in vitro acid detergent fibre digestibility in both silages (p < 0.05). In *P. eryngii* silage, L increased in vitro dry matter digestibility (p < 0.05), and both L and E increased in vitro hemicellulose digestibility (p < 0.05).
Aerobic stability results were directionally different by silage type. In *F. velutipes* silage, L and M improved aerobic stability by 24 h versus control (p < 0.05), and E improved it by 18 h (p < 0.05). In *P. eryngii* silage, M improved aerobic stability by 6 h versus control (p < 0.05), but L reduced aerobic stability by 42 h and E reduced it by 48 h (both p < 0.05). The authors also described the best aerobic stability times for the M groups as 96 h in *F. velutipes* silage and 138 h in *P. eryngii* silage.
CLINICAL IMPLICATIONS
This is not a clinical study, so direct human or veterinary clinical application is limited. However, for animal production systems, the findings suggest that combined lactic acid bacteria plus cellulase is a practical strategy to improve fermentation quality and aerobic stability of mushroom-derived silage, while cellulase is particularly useful for improving in vitro digestibility of *P. eryngii* silage. The authors emphasized that in vivo studies are still needed before recommending cellulase-treated *P. eryngii* silage for beef cattle fattening.