Abstract:

[Objective] This study was conducted to investigate the effects of high-concentrate diets on ruminal methanogens. [Method] Metagenomics and bioinformatic methods were used to investigate the impacts of high-concentrate diets on ruminal methanogens in dairy cows. [Results] Daily dry matter intake and milk production of cows offered high-concentrate diets were significantly lower than those of cows offered control diets (P < 0.05). Acetate concentration and ruminal pH decreased significantly while propionate and ammonia nitrogen concentrations were significantly increased in the rumens of cows fed high-concentrate diets, when compared with those in the control group (P < 0.05). Four classes, 36 genera and 108 species of methanogens were identified in this study and the relative abundance of methanogens was about 0.37%-0.47% of the entire rumen microbiome. Of these, Methanobacteria was the dominant genus, accounting for about 50%-55% of all methanogens, while Thermoplasmata was the second most abundant genus, accounting for about 31%. Feeding high-concentrate diets significantly decreased the relative abundance of all methanogens, Methanobacteria and Methanopyri (P<0.05). However, Methanococci and Methanomicrobia were not affected. Moreover, methanogens were positively correlated with acetate concentration and negatively correlated with propionate and ammonia nitrogen concentrations. [Conclusion] Feeding high-concentrate diets could reduce the relative abundance of methanogens; however, overfeeding of such diets may lead to low ruminal pH and subacute ruminal acidosis (SARA). Metagenomic methods used in this study accurately quantified the species and relative abundance of methanogens. The results presented herein will contribute to methane emission mitigation and improved dairy cattle production efficiency.

Key words: Dairy cows, High-concentrate diets, Methanogens, Metagenome, Bioinformatics