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

This study compared the potential of three white-rot fungi (<i>Pleurotus</i> 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 <i>P. ostreatus</i> (isolates P1 and P3) and <i>P. pulmonarius</i> (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 <i>in vitro</i> 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 <i>Pleurotus</i> 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. <i>Pleurotus</i> 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. <i>P. pulmonarius</i> had the highest DMD and lowest fiber content among the isolates tested and improved energy and nutrient utilization.