Effects of high-purity tribromoethanol (TBE) on methane production and ruminal fermentation across diets with different nutrient compositions using an in vitro gas production system

Ruminants contribute to climate change primarily through enteric methane (CH₄) production, prompting interest in developing feed additives to reduce CH₄ production. This study evaluated high-purity tribromoethanol (TBE) as a feed additive for reducing predicted CH₄ production , determining the optimal inclusion level and possible interactions with diet composition. The experiment consisted of three 48-h incubations using an in vitro gas production technique. Treatments were arranged in a 2 × 4 factorial design, with three replicates per treatment in each run. Treatments were two diets [low-fat, low-fiber, high-starch diet and high-fat, high-fiber, low-starch diet] and four inclusion levels of TBE [0, 20, 25, and 30 mg/kg dry matter (DM)]. Gas production was continuously recorded, and CH₄ concentration was measured at 2, 4, 8, 24, and 48 h of incubation. In vitro gas data were used to predict CH₄ production (mL/g DM) in vivo using a modeling approach. At 48 h, liquid samples and residues were collected for volatile fatty acid analysis and in vitro true DM degradability. No interactions were observed between diet and TBE inclusion level for any key parameter. Predicted total gas, predicted CH₄ production, and ratio of predicted CH₄ to total gas decreased linearly as TBE dose increased ( P ≤ 0.001). In vitro true DM degradability and total volatile fatty acid production were unaffected by TBE, whereas acetate proportion decreased and propionate increased linearly and quadratically with TBE inclusion ( P ≤ 0.004 and P ≤ 0.001). In conclusion, TBE supplementation at 30 mg/kg DM, reduced predicted in vivo CH₄ production by 28.4%, without adverse effects on in vitro ruminal fermentation or degradability. The efficacy of TBE was not influenced by the diet composition in this study. Further in vivo studies are required to confirm the long-term impact on both enteric CH₄ production and ruminant's performance.