Capsaicin Modulates Ruminal Fermentation and Bacterial Communities in Beef Cattle with High-Grain Diet-Induced Subacute Ruminal Acidosis.

This study was developed with the goal of exploring the impact of capsaicin on ruminal fermentation and ruminal bacteria in beef cattle affected by high-grain diet-induced subacute ruminal acidosis (SARA). In total, 18 healthy Simmental crossbred cattle were randomized into three separate groups ( = 6/group): (1) control diet (CON; forage-to-concentrate ratio = 80:20); (2) high-grain diet (SARA; forage-to-concentrate ratio = 20:80); and (3) high-grain diet supplemented with capsaicin (CAP; 250 mg/cattle/day). The study was conducted over a 60-day period. The results showed that the SARA model was successfully induced in the SARA group with a high-grain diet. Relative to the SARA group, the addition of capsaicin elevated the ruminal pH from 5.40 to 6.36 ( < 0.01), and decreased the total volatile fatty acids (VFAs) from 133.95 to 82.86 mmol/L ( < 0.01), aligning closely with the levels observed in the CON group. The addition of capsaicin increased the alpha diversity of ruminal bacteria relative to the SARA group, as evidenced by a lower Simpson index ( < 0.05), together with increases in the Ace, Chao, and Shannon indices ( < 0.05). Bacteroidota and Firmicutes were the most common phyla across all treatment groups, while was the predominant genera. The unique bacterial genera (LDA scores > 4) identified within the SARA group comprised , , , , and , which may serve as potential biomarkers for the diagnosis of SARA. The unique genera associated with the CON group included , , and , while those for the CAP group included and . In summary, these results suggest that dietary capsaicin supplementation can limit the adverse effects of SARA through the modulation of bacterial communities within the rumen, thus altering ruminal fermentation in beef cattle.