Effects of plant-based fermented broth on rumen fermentation, gastrointestinal development, and microbial populations in fattening lambs.

Introduction: Digestive dysfunction in lamb fattening has been a concern in recent years. The objective of this study was to investigate the effects of a fermentation broth (FB) derived from eight plants on rumen fermentation, gastrointestinal development, and microbial community composition in fattening lambs through in vitro and in vivo experiments.

Methods: In vitro rumen fermentation was performed with six FB: diet ratios (mL/g): 0, 1:125, 1:250, 1:500, 1:1000, and 1:2000. Fermentation parameters and nutrient disappearance rates were measured over 48 h. Based on the results of the in vitro test, two optimal doses of FB (1:500 and 1:1000) were selected for further in vivo testing over a 120-day period. A total of 90 weaned small-tailed Han lambs were assigned to three groups, receiving FB in drinking water at 0 (control), 1:500, or 1:1000 (vol/vol).

Results: The results showed that three parameters of gas production (GP), including fast-degradable fraction, slow-degradable fraction, and theoretical GP, were significantly higher (p < 0.05) in the 1:500 and 1:1000 groups compared with other groups. In vivo tests further showed that FB supplementation at 1:500 and 1:1000 improved rumen microstructure (papilla length, papilla surface, mucosa thickness, and muscle thickness) and jejunal microstructure (villus height, villus surface, and muscle thickness). Moreover, two rumen bacterial indices, PD_whole_tree (p = 0.06) and Shannon (p = 0.07), demonstrated increasing trends in both FB groups relative to the control group. In the rumen, 1:500 FB supplementation increased the abundance of Firmicutes (p < 0.01) and decreased Bacteroidota abundance (p < 0.01). In the jejunum, 1:500 FB supplementation decreased the abundance of Euryarchaeota and Methanobrevibacter (both p = 0.02) while increasing the abundance of Actinomycetes and Aeriscardovia (both p = 0.01) compared to the control.

Discussion: In summary, FB supplementation in lambs' drinking water at a ratio of 1:500 (FB: diet, mL/g) improved rumen fermentation and promoted microecological balance.