Specific enrichment of microbes and increased ruminal propionate production: the potential mechanism underlying the high energy efficiency of Holstein heifers fed steam-flaked corn
Abstract Corn grain is high in starch content and is primarily used as an energy source in ruminant diets. Compared with finely ground corn (FGC), steam-flaked corn (SFC) processing could improve the milk yield of lactating dairy cows and the growth performance of feedlot cattle, but the detailed mechanisms underlying this finding are unknown. The rumen microbiome contributes to feed efficiency by breaking down feedstuffs into energy substrates that can subsequently be utilized by the host animal. Therefore, the current study was conducted to investigate the ruminal bacterial community of heifers fed differently processed corn (SFC or FGC) with the same forage-to-concentrate ratio using 16S rRNA sequencing technologies and to uncover the detailed mechanisms underlying the high performance of ruminants fed the SFC diet. The results revealed that different processing methods resulted in changes in rumen characteristics and impacted the composition of the rumen bacterial structure. The SFC diet resulted in an increased average daily gain in heifers, an increased rumen propionate concentration and a decreased ammonia nitrogen concentration. The relative abundance of the phylum Firmicutes tended to increase and the relative abundance of the phylum Proteobacteria significantly increased in the heifers fed SFC diet compared with FGC diet. In addition, the relative abundance of amylolytic bacteria of the genera Succinivibrio , Rosebuia and Blautia ere evaluated, and cellulolytic bacteria (Ruminococcaceae_UCG-014 and Ruminococcaceae_UCG-013 ) decreased by the steam flaking method. Spearman correlation analysis between the relative abundances of the ruminal bacteria and the microbial metabolites showed that the rumen propionate concentration was positively correlated with Succinivibrio and Blautia abundance and negatively correlated with Ruminococcaceae_UCG-014 abundance. Evident patterns of efficient improvement in rumen propionate and changes in rumen microbes to further improve feed conversion were identified. This observation uncovers the potential mechanisms underlying the increased efficiency of the SFC processing method for enhancing ruminant performance.