Solid state fermentation: A strategy for wheat bran supplemented corn stover valorization with Pleurotus species

This study compared the potential of three white-rot fungi (Pleurotus spp.) to enhance the nutritional value of corn stover as a feed resource for ruminants. A mixture of shredded corn stover and wheat bran (ratio 9:1) was moisturized (65%), loaded into polypropylene bags, and sterilized at 121 °C for 1 h. Four replicate bags were each inoculated with P. ostreatus (isolates P1 and P3) and P. pulmonarius (isolate P2) and incubated at 25 °C for 0, 2, 4, 6, and 8 weeks. After inoculation and incubation of the corn stover, the resultant substrates and rumen fluid obtained from three ruminally cannulated beef cows were investigated using an in vitro batch culture study, designed as a 3 × 5 factorial with six replicates. Results revealed a significant (p < 0.001) effect on dry matter digestibility (DMD), with the highest DMD observed at 8 weeks for all Pleurotus isolates tested. The best (p < 0.001) performance was seen in corn stover treated with P2 at weeks 6 and 8. Additionally, P1 at 0 and 6 weeks had the lowest ash and highest (p < 0.001) organic matter (OM) concentrations, respectively, compared to P2 at 8 weeks, which had the highest ash and the lowest OM concentrations. The highest (p = 0.011) crude protein (CP) content was recorded in P1 at week 8, while P1 at week 0 had the lowest CP content. Compared to untreated corn stover, higher (p < 0.001) acid detergent fiber digestibility was recorded in corn stover treated with P2 at 8 weeks, while higher (p < 0.001) neutral detergent fiber digestibility was observed in P3 at 2 weeks. Pleurotus strains and incubation periods affected microbial mass production (p < 0.001), with minimal effects on total and individual volatile fatty acids. However, P3 at 2 weeks increased (p = 0.035) acetate and decreased (p = 0.001) propionate proportions. The results indicate that different isolates affected corn stover differently, but in general, all isolates improved the nutritional value of corn stover. P. pulmonarius had the highest DMD and lowest fiber content among the isolates tested and improved energy and nutrient utilization.