Chemical composition, microbial community, and fermentation characteristic of sweet sorghum straw fermented with sheep rumen fluid by in vitro method.

This study aimed to explore how pre-treatment with rumen fluid and the duration of anaerobic fermentation of sweet sorghum (SS) straw affect the nutritional constituents, fermentation characteristics, and microbial community. Various amounts of diluted rumen fluid (0, 10, 20, and 30 mL per 100 g of SS straw) were mixed with the straw to produce fermented feed with a target moisture content of 75 %. The sampling and analysis were conducted on days 0, 15, and 45, respectively. With the increasing anaerobic fermentation time and amount of rumen fluid, the contents of dry matter (DM), water-soluble carbohydrates, neutral detergent fibre, acid detergent fibre, acid detergent lignin, cellulose, and ammonia nitrogen and pH value of SS straw exhibited an overall decreasing trend, whereas the contents of crude protein (CP), lactic acid (LA), and acetic acid (AA) exhibited an overall increasing trend (P < 0.01). The interaction effect of amount of rumen fluid and fermentation time on the chemical components and fermentation parameter indicators of SS straw was highly significant (P < 0.01). At the phylum level, Firmicutes were enriched, and at the genus level, the abundance of Lactobacillus and Weissella increased with the increasing concentration of rumen fluid and fermentation time. On day 15, Ruminococcus, Prevotella, and Bifidobacterium exhibited significant positive correlations with CP, LA, and AA (P < 0.01). By day 45, Weissella and Bacillus were negatively correlated with CP but positively with DM (P < 0.01), whereas Lactobacillus exhibited an opposite trend. Additionally, LA and AA levels were significantly negatively correlated with Bacillus (P < 0.01). Therefore, treatment of SS straw with rumen fluid significantly impacted its chemical composition, fermentation characteristics, microbial community, and their correlations, providing a scientific basis for the practical application of rumen-fluid-fermented straw feed.