Molecular hydrogen produced by elemental magnesium inhibits rumen fermentation and enhances methanogenesis in dairy cows

Abstract

Hydrogen is a key metabolite that connects microbial fermentation and methanogenesis in the rumen. This study was to investigate the effects of elevated H 2 produced by elemental Mg on rumen fermentation and methanogenesis in dairy cows. Four nonlactating Chinese Holstein dairy cows were employed for this experiment in a replicated crossover design. The 2 dietary treatments included a basal diet supplemented with Mg(OH) 2 (14.5 g/kg of feed dry matter) or elemental Mg (6.00 g/kg of feed dry matter). When compared with Mg(OH) 2 treatment, cows fed diet with elemental Mg had similar rumen Mg 2+ concentration, but higher rumen dissolved H 2 and methane concentrations at 2.5 h after morning feeding. Also, elemental Mg supplementation decreased feed digestibility, rumen volatile fatty acid concentration, and relative abundance of group Ruminococcaceae_UCG-014, genus Bifidobacterium, and group Mollicutes_RF9, increased acetate to propionate ratio, succinate concentration, and abundance of family Christensenellaceae. Elemental Mg supplementation increased enteric CH 4 emission, altered methanogen community with increased abundance of order Methanomassiliicoccales, 16S ribosomal RNA gene copies of methanogens, and order Methanobacteriales. In summary, the pulse of elevated dissolved H 2 after feeding produced by elemental Mg inhibited rumen fermentation and feed digestibility by decreasing the abundance of carbohydrate-degrading bacteria, promoted H 2 incorporation into succinate by increasing family Christensenellaceae and genus Bacteroidales_BS11, and increased H 2 utilization for methanogenesis by favoring growth of methanogens.