Effect of active and heat-killed Clostridium butyricum on in vitro gas production, ruminal fermentation, and microbiota varying with pH levels.

Abstract

Objective: : The objective of this study was to evaluate the effects of inactive (heat-killed) Clostridium butyricum (ICB) on gas production kinetics, fermentation parameters, and microbiota with varying media pH levels in batch culture.

Methods: : The in vitro experiment was designed as a completely randomized factorial arrangement, with 2 media pH levels (5.8 and 6.5) × 2 CB products (active and inactive) × 4 dosages. Two lactating dairy cows with ruminal fistulas, fed a diet comprising 40% forage and 60% concentrate, served as donors for rumen inoculum. Following 24 h of incubation, the gas production, dry matter disappearance (DMD), volatile fatty acid (VFA), ammonia nitrogen (NH3-N) and microbial profile were analyzed to determine the effect of treatment on fermentation.

Results: : The gas volume (GV), DMD, total VFA concentration, NH3-N concentration, acetate proportion and microbial alpha diversity were inhibited when the media pH decreased from 6.5 to 5.8. Increasing the supplemental doses of ICB linearly increased the GV, DMD (trend) and butyrate proportion at media pH 6.5. Moreover, the increasing supplemental dose of active Clostridium butyricum (ACB) linearly increased GV, butyrate proportion and NH3-N concentration (trend) regardless of media pH, and linearly increased DMD, total VFA concentration and A:P ratio at media pH 6.5. Supplementing ICB decreased the relative abundance of Actinobacteria and Butyrivibrio in the fermentation fluid.

Conclusion: s: Increasing media pH would favor rumen fermentation and alter bacterial community. Although both ACB and ICB have the potential to stimulate rumen fermentation in a dose-dependent manner, their effects vary with different media pH levels. Moreover, both ACB and ICB rarely caused changes to the rumen bacterial community.