This experiment investigated the effects of rumen-protected leucine (RP-Leu) supplementation on growth performance, rumen fermentation parameters, and rumen microbiota of fattening sheep. Forty fattening sheep (19.03 ± 0.38 kg) were randomly divided into four groups. The four groups were fed the basal diet supplemented with RP-Leu at 0 (L-0), 0.5 (L-0.5), 1.0 (L-1.0), or 1.5 (L-1.5) g/d. The experimental period lasted 67 d. The results demonstrated that compared with the L-0 group, the L-1.0 and L-1.5 groups significantly increased the average daily gain (ADG) by 22.2% and 18.0%, respectively (p < 0.05), and reduced the feed-to-gain ratio (F:G ratio) by 20.0% and 13.4% (p < 0.05); the L-1.5 group significantly increased the concentrations of propionate and isovalerate (p < 0.05) and significantly decreased the acetate to propionate ratio (A:P) by 25.7% (p < 0.05); and the L-1.0 group significantly decreased the concentrations of free branched-chain amino acids (BCAAs) in rumen (p < 0.05). A microbiota analysis showed that RP-Leu enriched the abundance of fiber-degrading bacteria. A correlation analysis showed that acetic acid and A:P were positively correlated with norank_f_F082 and norank_f_UCG-011 (p < 0.05). Phenylalanine, isoleucine, valine, and leucine were negatively correlated with norank_o_Bacteroidales (p < 0.05). In conclusion, RP-Leu improved the growth performance of fattening sheep by changing the rumen fermentation parameters and patterns; the optimal supplementation level is 1.0 g/d.

Cottonseed meal (CSM), an important protein-rich feed ingredient, faces limited utilization in livestock diets due to the presence of free gossypol (FG)—a potent antinutritional toxin. This study aimed to isolate FG-degrading bacteria from the cotton bollworm, Helicoverpa armigera, and to evaluate their potential as probiotics in vitro. Eleven gossypol-tolerant strains were isolated from the gut of Helicoverpa armigera larvae using a screening medium containing gossypol as the sole carbon source. Among these, four lactic acid bacteria strains—Pediococcus acidilactici GM-NP, Pediococcus acidilactici GM-P, Enterococcus faecalis GM-6, and Weissella confusa GM-2—were selected for further investigation of their gossypol degradation capacity and probiotic potential. Probiotic characterization revealed that all strains exhibited tolerance to gastrointestinal fluids and bile salts, safe γ-hemolysis, and strong auto-aggregation, cell surface hydrophobicity, and antimicrobial activity. Solid-state fermentation of CSM with these strains reduced FG content by more than 50%, increased crude protein by over 6%, and elevated acid-soluble protein content by more than 70%, thereby effectively enhancing the nutritional quality of CSM. This study is the first to demonstrate that bacterial isolates from the gut of Helicoverpa armigera possess concurrent high-efficiency gossypol degradation and probiotic properties, providing a theoretical foundation for developing novel probiotic resources and promoting the safe utilization of CSM.

The optimal timing for initiating starter feeding in lambs remains controversial, warranting a systematic evaluation of its effects across multiple indicators. This study investigated the effects of initiating starter feeding at 7, 14, or 21 days of age on growth performance, rumen fermentation, serum immunity, gastrointestinal development, and microbiota in Hu lambs. Forty-five newborn lambs were randomly assigned to three groups (n = 15 per group) and fed starter until slaughter at weaning (60 days). The 14-day group exhibited significantly higher body weight (BW) at 49 and 60 days compared with the 7-day group (p < 0.05), and greater average daily gain (ADG) during 28–35 days than the 21-day group. Rumen ammonia nitrogen (NH₃-N), acetate, propionate, valerate, and total volatile fatty acids (VFAs) were higher in the 7-day and 14-day groups than in the 21-day group (p < 0.05). The 14-day group showed lower pro-inflammatory cytokines (IL-1β, TNF-α) and higher immunoglobulins (IgA, IgG, IgM) and anti-inflammatory cytokines (IL-2, IL-4) (p < 0.05). This group also displayed improved rumen papilla width, jejunal villus dimensions, and reduced crypt depth. Beneficial microbes such as Christensenellaceae_R-7_group and Butyrivibrio were enriched in the 14-day and 21-day groups. In conclusion, initiating starter feeding at 14 days of age optimizes growth, rumen function, immune response, and colonization of beneficial microbiota in Hu lambs.