ABSTRACTBackgroundRecent studies using batch-fermentation suggest that the red macroalgaeAsparagopsis taxiformismight reduce methane (CH4) emission from beef cattle by up to ~99% when added to rhodes grass hay, a common feed in the Australian beef industry. These experiments have shown significant reductions in methane without compromising other fermentation parameters (i.e. volatile fatty acid production) withA. taxiformisorganic matter (OM) inclusion rates of up to 5%. In the study presented here,A. taxiformiswas evaluated for its ability to reduce methane production from dairy cattle fed a mixed ration widely utilized in California; the largest milk producer in the US.ResultsFermentation in a semi-continuousin-vitrorumen system suggests thatA. taxiformiscan reduce methane production from enteric fermentation in dairy cattle by 95% when added at a 5% OM inclusion rate without any obvious negative impacts on volatile fatty acid production. High-throughput 16S ribosomal RNA (rRNA) gene amplicon sequencing showed that seaweed amendment effects rumen microbiome communities consistent with the Anna Karenina hypothesis, with increased beta-diversity, over time scales of approximately three days. The relative abundance of methanogens in the fermentation vessels amended withA. taxiformisdecreased significantly compared to control vessels, but this reduction in methanogen abundance was only significant when averaged over the course of the experiment. Alternatively, significant reductions of methane in theA. taxiformisamended vessels was measured in the early stages of the experiment. This suggests thatA. taxiformishas an immediate effect on the metabolic functionality of rumen methanogens whereas its impact on microbiome assemblage, specifically methanogen abundance, is delayed.ConclusionsThe methane reducing effect ofA. taxiformisduring rumen fermentation makes this macroalgae a promising candidate as a biotic methane mitigation strategy in the largest milk producing state in the US. But its effectin-vivo(i.e. in dairy cattle) remains to be investigated in animal trials. Furthermore, to obtain a holistic understanding of the biochemistry responsible for the significant reduction of methane, gene expression profiles of the rumen microbiome and the host animal are warranted.
Effect of the macroalgaeAsparagopsis taxiformison methane production and the rumen microbiome assemblage
