Methanogenesis inhibition by bacitracin via modulating rumen microbial composition as demonstrated in in vitro assays

This study aimed to assess how bacitracin (BAC) affects rumen fermentation, methane production, and the microbial community during a 24-h in vitro incubation with diets in different forage:concentrate ratios. In experiment 1, we determined the optimal BAC dosage by adding 0 to 400 mg/kg of BAC to 3 diets: high-concentrate (0.1 forage:0.9 concentrate), medium-concentrate (0.5 forage:0.5 concentrate), and low-concentrate (0.9 forage:0.1 concentrate). Experiment 2 evaluated the interaction between BAC (0 mg/kg and 100 mg/kg) and different forage:concentrate ratio diets. Experiment 3 focused on the effect of BAC (0 mg/kg and 100 mg/kg) on rumen microbial composition in a high-concentrate diet. Results showed that adding BAC to diets with different concentrate ratios significantly reduced rumen methane production, with 100 mg/kg being the optimal dosage for all 3 diets. An interaction between BAC and concentrate diet proportion was observed in methane production: The addition of BAC to the high-concentrate diet resulted in the most pronounced reduction in methane production, with decreases of 20.52%, 9.34%, and 1.31% for the high-, medium-, and low-concentrate diets, respectively. Further examination of the rumen microbial community in high-concentrate diet groups revealed that at the bacterial level, BAC supplementation significantly decreased the relative abundance of the Rikenellaceae RC9 gut group and Christensenellaceae R7 group, while increasing that of Ruminobacter and Succinivibrio. At the archaeal level, BAC significantly reduced the relative abundance of Methanobrevibacter and Methanobrevibacter ssp. YE315. These findings indicate that BAC has the potential to inhibit rumen methanogenesis.