Due to implications of global climate changes, greenhouse gas (GHG) emissions coming from the livestock industries have been the topic of ongoing investigations. Several studies have looked at feeding seaweeds to assess their impact on methanogenesis in ruminants. Natural volatile halomethanes found in some seaweeds have been shown to inhibit rumen methanogenesis.
In this experiment, 6 different species of seaweed; Sargassum horneri (SH), Ecklona arborea (EA), Ascophyllum nodosum (AN), Sargassum fluitans (SF), Mastocarpus papillatus (MP), and Fucus vesiculosus (FV), were analyzed for their effect on gas production and composition, volatile fatty acid (VFA) production, and neutral detergent fiber (NDF) degradability in vitro. Incubations were duplicated and carried out for 24h with inoculum taken from two cannulated lactating Holstein cows fed a standard corn silage/alfalfa haylage and concentrate feeds diet. Treatments were tested in triplicate, at an inclusion rates of 0.5, 1.0, and 2.0% of feed dry weight (DW). Asparagopsis taxiformis (AT) has known antimethanogenic properties and was used as a positive control at 1% DW. Gas samples were collected at 12 h and 24 h and analyzed for methane (CH4) and hydrogen (H2) concentrations. VFA production and NDF degradability were analyzed at incubation termination. Compared with the negative control (NCON; i.e., animal feed without seaweed) at 12 h, none of the treatments decreased CH4 production. Relative to NCON at 24 h, SH decreased (P = 0.01; SEM = 0.6) CH4 production by 15% (8.9 vs. 7.6 mL/g of feed DW, respectively). Methane production was increased, compared with NCON, by MP and SF (P ≤ 0.04, SEM = 0.6; 10.0 and 9.9 mL/g of feed DW, respectively). In line with previous research in our laboratory, AT decreased (P < 0.01) CH4 production by 98% compared with NCON. Hydrogen production was negligible (average of 0.01 mL/g feed DW) for all treatments, except AT, which averaged 2.0 mL/g of feed DW (P < 0.001). Compared with NCON, MP and FV increased (P ≤ 0.05; SEM = 5.3) total VFA concentration (65.2, 76.4 and 74.3 µmol/mL, respectively) and MP also increased (P = 0.02; SEM = 3.1) acetate concentration (34.5 vs. 40.6 µmol/mL). Proprionate concentration was increased by MP and FV (P ≤ 0.02; SEM = 1.8) when compared with NCON (24.3, 23.9, and 20.5, respectively). There was no effect of seaweed on molar proportions of VFA, acetate: propionate ratio, and NDF degradability. Overall, except the positive control Asparagopsis taxiformis and Sargassum horneri (15% reduction at 24 h), seaweed species tested in this in vitro experiment did not influence enteric methane production. Some species (Mastocarpus papillatus and Fucus vesiculosus) appeared to have a positive effect on rumen fermentation by increasing total VFA and acetate and/or proprionate concentrations.