Abstract
BackgroundThe rumen bacterial community plays a critical role in feeds degradation and productivity. The effects of different forage to concentrate ratios on the ruminal microbial population structure have been studied extensively; however, research into changes in the ruminal bacterial community composition in heifers fed different energy level diets, with the same forage to concentrate ratio, has been very limited. The purpose of this study was to investigate the effects of different dietary energy levels, with the same forage to concentrate ratio, on ruminal bacterial community composition of heifers. Furthermore, we also determine the relationship between rumen bacteria and ruminal fermentation parameters.ResultsThe 16S rRNA gene sequencing showed that, under the same forage to concentrate ratio of 50:50, an 8% difference in dietary energy level had no significant impact on the alpha diversity and the relative abundance of the major phyla and most of the major genera in heifers. In all the treatments groups, Firmicutes, Bacteroidetes, and Proteobacteria were the dominant phyla. Spearman correlation analysis between the relative abundances of the rumen bacteria at the genus level and the fermentation parameters showed that the relative abundances of Prevotella and BF311 were positively correlated with the ammonia nitrogen and butyrate concentrations, and these two genera were negatively correlated with the propionate and isovalerate concentrations, respectively, and the genus Bifidobacterium was positively correlated with the butyrate concentration and was negatively correlated with propionate and isovalerate concentration. The total volatile fatty acid concentration was positively correlated with BF311 abundances, and was negatively correlated with Trichococcus and Facklamia abundances.ConclusionsUnder the same forage to concentrate ratio condition of 50:50, an 8% difference in dietary energy levels had little impact on rumen bacterial community composition in heifers. The correlations between some genera of ruminal bacteria and the concentrations of volatile fatty acids and ammonia nitrogen might be indicative that the ruminal fermentation parameters are strongly influenced by the rumen bacterial community composition.
Highlights
The rumen bacterial community plays a critical role in feeds degradation and productivity
Sequencing depth, coverage, and alpha diversity After data filtering, quality control, and chimera removal, a total of 3,466,038 V3–V4 16S ribosomal ribonucleic acid (rRNA) sequence reads from the 36 samples were generated, with a mean of 96,279 sequence reads for each sample
Under the same forage to concentrate ratio condition of 50:50, an 8% difference in dietary energy levels had no significant impact on rumen bacterial community composition in heifers
Summary
The rumen bacterial community plays a critical role in feeds degradation and productivity. The effects of different forage to concentrate ratios on the ruminal microbial population structure have been studied extensively; research into changes in the ruminal bacterial community composition in heifers fed different energy level diets, with the same forage to concentrate ratio, has been very limited. The ruminal microorganisms play an important role in degrading complex feeds into volatile fatty acids (VFA) and ammonia, and synthesizing vitamin B and microbial cell protein, which are critical for animal health and production performance [2,3,4]. During adaptation to a high-grain diet from a high-forage diet, significant changes in the rumen bacterial population structure and major fermentation products have been reported [10,11,12]. A previous study showed that changes in the ruminal microbial population structure could help promote feed efficiency and mean daily gain in cattle [14]
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