Methane reduction potential of brown seaweeds and their influence on nutrient degradation and microbiota composition in a rumen simulation technique

This study aimed to investigate the effect of two Icelandic seaweed samples (Ascophyllum nodosum and Fucus vesiculosus) on in vitro methane production, nutrient degradation, and microbiota composition. Both seaweeds were used at two inclusion levels (2.5 and 5% of ration dry matter) in the long term rumen simulation technique Rusitec. Seaweeds were incubated over a period of 14 days together with a total mixed ration, which was also used as control treatment. Methane concentration of total gas production was significantly reduced by the supplementation of both seaweeds at the higher inclusion with a higher reduction caused by the A. nodosum sample. The observed reduction in methane concentration was lower than previously reported for the red seaweed Asparagopsis taxiformis. Total gas production was reduced by all seaweed supplements with a higher reduction for the higher seaweed inclusion levels. Feed nutrient degradation, and the production of volatily fatty acids and NH3-N in the effluent were also reduced, mostly with a bigger effect for the 5% inclusion level of both seaweed supplements, indicating a reduced overall fermentation. Because of high iodine content in the seaweeds tested, the application in practical feeding should be applied with caution. For the analyzes of microbiota composition in starting material, fermenter liquid and effluent on day 7 and 14 and feed residues on day 14, total nucleic acids were extracted and the 16S rRNA gene was targeted for use in the amplicon sequencing process. The microbiota composition differed not only between the rumen fluid used for the start of incubation and the samples taken on day 7 but also after the adaptation period between day 7 and 13 in fermenter liquid and effluent. This could indicate that adaptation of the microbes to the system was not finalized after day 7. In effluent and fermenter liquid samples, archaeal and bacterial amplicon sequence variants were separated into two groups. One was more abundant in samples taken from the treatment without seaweed supplementation. The other one prevailed in seaweed supplemented treatments. This group also showed a dose dependent response to seaweed inclusion, with a stronger difference between the 5% inclusion level and the unsupplemented samples than the 2.5% inclusion level.