Growth Performance and Rumen Microbiota of Sheep Respond to Cotton Straw Fermented with Compound Probiotics

To develop cotton straw as a feed resource through biological fermentation, it was fermented using compound probiotics (Bacillus subtilis, Saccharomyces cerevisiae, and Lactobacillus plantarum) and subsequently fed to sheep after the nutrients and hygienic indices of the fermented cotton straw (FCS) were analyzed. Sixty sheep were randomly assigned to five groups: a control group (CON); a low-proportion fermented cotton straw group (LFC, with FCS comprising 14.5% of the diet); a high-proportion fermented cotton straw group (HFC, with FCS comprising 29.0% of the diet); a compound microbial group (MIC, containing Bacillus licheniformis, Bacillus subtilis, and yeast); and a microbial-enzymatic preparation group (MEY, containing compound probiotics and enzymes such as cellulase, xylanase, β-glucanase, amylase, and protease). The trial lasted seven weeks and was divided into two stages: stage 1 (weeks 1–4, days 1–28) and stage 2 (weeks 5–7, days 29–49). Body weight and daily feed intake were registered, and blood and rumen fluid samples were obtained at day 28 and day 49 of the feeding trial. Fermentation significantly increased the crude protein content of cotton straw while reducing neutral detergent fiber (NDF) and acid detergent fiber (ADF) (p < 0.05). Additionally, fermentation reduced the residues of aflatoxin B1, vomitoxin, zearalenone, and free gossypol in the treatment groups (p < 0.05). LFC possessed the lowest value of feed-to-gain ratio (F/G) among all groups. Serum indices related to antioxidant capacity and utilization of fat and protein increased in the treatment group (p < 0.05). Rumen microbiota were separated between different groups (p < 0.05). LFC and HFC enhanced the abundance of Prevotella. These findings could provide conclusions that fermented cotton straw has the tendency to enhance the growth performance of sheep by increasing the abundance of bacteria related to utilization of protein, carbohydrate, and other nutrients such as Prevotella, in which the LFC group has the best fast-fattening (about 50 d) effect.