Optimizing solid-state fermentation conditions of cotton stalks with Cohnella xylanilytica sp. to improve nutritive value of cotton stalks and rumen fermentation

The solid-state fermentation conditions of cotton stalks using xylanolytic Cohnella xylanilytica sp. strain T5 were optimized, using the true protein (TP) content as an indicator in a one-way test with a six-factor, three-level L₉ (3⁴) orthogonal experimental design. The changes in nutrient, mycotoxin, and free gossypol contents before and after fermentation were compared for a control group (no fermentation) and a fermentation group (optimal fermentation conditions). A 72 h in vitro fermentation test was conducted using the in vitro gas production method to compare the changes in gas production, pH, volatile fatty acid, and ammoniacal nitrogen concentration between the control and fermentation groups. The results showed that 1) the optimal cotton stalk fermentation conditions were a temperature of 30 ℃, a duration of 8 d, a material-water ratio of 1:0.9, as well as seed liquor, cornmeal, and urea additions of 6.20 × 10⁶ cfu∙g⁻¹, 15%, and 2%, respectively. 2) The TP and crude protein contents of the fermentation group were significantly higher by 111.96% and 19.44%, respectively (P < 0.05), and the neutral and acid detergent fiber contents were significantly lower (P < 0.05). under the optimal fermentation conditions compared with those in the control group The free cholesterol content was significantly lower by 13.73% (P < 0.05) and the zearalenone, deoxynivalenol, and aflatoxin B₁ contents were lower than those in China’s Feed Hygiene Standard. 3) The in vitro fermentation test showed that the ammoniacal nitrogen, microbial protein, and volatile fatty acid concentrations were significantly higher in the fermentation group than in the control group (P < 0.05). In summary, the fermented cotton stalks had a markedly improved nutrient composition, and their mycotoxin levels were within the national standard limits. Fermented cotton stalks can be applied for promoting rumen fermentation.