Increasing Buffering Capacity Alters Rumen Microbiota Composition and Enhances Rumen Fermentation Characteristics of High-Concentrate Fed Hanwoo Steers
Abstract Background: Rumen bacterial community is mainly affected by the type of diet consumed by the host animals. High concentrate diet increases the abundance of lactic acid producers and utilizers due to high level of non-structural carbohydrates thus reducing the number of fiber-degrading bacteria because of drastic decrease in pH. Dietary buffers are essential in regulating rumen pH through the compounds responsible in resisting drastic decrease in pH once cattle were fed with high-concentrate diet. However, no study has evaluated the effects of buffering capacity and efficiency in alleviating chronic acidosis in rumen. Ruminal metataxonomic and fermentation characteristics analyses were conducted to evaluate the effect of different buffering capacities on in vitro and in vivo experiments in high-concentrate fed Hanwoo steers. Results: Results revealed that BC0.9% and BC0.5% had similar and significant effect (P < 0.05) on in vitro ruminal fermentation at 3 to 24 h incubation. Both BC0.9% and BC0.5% had significantly highest (P < 0.05) buffering capacity, pH, and ammonia-nitrogen (NH3-N) than BC0.3% and CON at 24 h of incubation. Individual and total volatile fatty acids (VFA) were significantly lowest in CON. Increasing buffering capacity concentration showed linear effect on pH at 6 to 24 h while total gas and NH3-N at 3 and 12 h. Phylum Bacteroidetes dominated all treatments but a higher abundance of Firmicutes in BC0.5% than others. Ruminoccocus bromii and Succiniclasticum ruminis were dominant in BC0.5% and Bacteroides massiliensis in BC0.3%. The normalized data of relative abundance of observed OTUs’ representative families have grouped the CON with BC0.3% in the same cluster, whereas BC0.5% and BC0.9% were clustered separately which indicates the effect of varying buffering capacity of buffer agents. Principal coordinate analysis (PCoA) on unweighted UniFrac distances revealed close similarity of bacterial community structures within and between treatments and control, in which BC0.9% and BC0.3% groups showed dispersed community distribution. Conclusion: Our findings showed that increasing buffering capacity enhances rumen fermentation parameters and affects rumen microbiome by altering bacterial community through distinct structure between high and low buffering capacity, thus an important factor contributed to the prevention of ruminal acidosis during a high-concentrate diet.