Improving the Nutritional Value and Safety of Cotton Stalk Feed via Response Surface Methodology and Co-Fermentation Techniques

Cotton stalks, a major agricultural byproduct, are challenging to decompose naturally; however, they can be transformed into valuable animal feed through microbial fermentation. This study identifies Aspergillus niger HQXY as the most efficient cellulase-producing strain out of six evaluated strains, using it to ferment cotton stalks and significantly degrade cellulose and hemicellulose. By optimizing solid-state fermentation conditions via response surface methodology, the crude fiber content of the cotton stalks was reduced by 34%. A novel sequential co-fermentation approach combining Aspergillus niger with probiotics (Bacillus licheniformis, Candida utilis, and Lactobacillus casei) further enhanced the feed’s nutritional profile. The optimal results were obtained using a 1:1:1 ratio of strains (Aspergillus niger, Bacillus licheniformis, and Lactobacillus casei) at a 8% inoculation rate over 30 days. This co-fermentation strategy lowered the pH and reduced gossypol to 15.5 mg·kg−1. The findings highlight the effectiveness of Aspergillus niger HQXY and probiotics in improving the quality of cotton stalks, by reducing crude fiber and gossypol content, thus offering a promising method for the sustainable utilization of agricultural waste as high-quality animal feed.