Effects of feeding dairy cows seaweed mixtures on feed intake, methane emission, milk production, and milk mineral and fatty acid composition.

There has been much recent research interest in the potential of macroalgae (seaweed) as a methane-suppressing feed supplement for ruminants, but there are numerous potential seaweed species available that have varying compositions of potentially beneficial or deleterious consequence. Therefore, the objective of the present study was to determine the effects of feeding 3 mixtures of 3 seaweeds at levels within EU regulatory limits for ration iodine concentration on methane production and milk yield and composition of dairy cows. Forty lactating (204 ± 5.6 DIM) Holstein cows were randomly assigned to 1 of 4 treatments (10 per treatment) in blocks based on DIM, parity, BW, and milk yield. Treatments were a control TMR and 1 of 3 seaweed mixtures replacing TMR grass silage: Ascophyllum nodosum, Fucus vesiculosus, and Asparagopsis taxiformis (AN, FV, and AT, respectively; 5:45:50 and 1.5 g/kg DM), AN and FV (AN:FV at 90:10 and 6.5 g/kg DM), or FV and AN (FV:AN at 90:10 and 17.5 g/kg DM). Cows were individually fed for ad libitum DMI in freestall housing and treatments continued for 7 wk, with daily measurements of milk yield and DMI and weekly measurements of milk composition. Methane emission was estimated using 2 GreenFeed head chambers in wk 5 to 7 of treatment, milk mineral concentrations were measured in wk 1 to 6, and milk FA composition was measured in wk 6. Feeding the AN:FV and FV:AN mixtures had no effect on methane emission (g/d) or yield (g/kg DMI), whereas cows fed AT (0.075% of DM) in combination with AN and FV tended to have a lower methane emission (9%) and methane yield (12%) than cows fed the control diet and lower (20%) methane intensity (g/kg ECM) than cows fed the AN:FV mixture. Cows fed all 3 seaweed mixtures had 1.7- to 2.2-fold higher milk iodine concentrations, which showed a week-by-treatment interaction, in that cows fed the AN:FV mixture had higher milk iodine concentrations in wk 3 and 5 of the study. Cows fed the AN:FV also had lower milk urea concentration, suggesting effects of AN or FV bioactive components on rumen protein degradation. Cows fed the AT:AN:FV mixture had lower concentrations of C18:3n6, and higher concentrations of C15:1 and C17:0, but there were no other effects of feeding seaweed on milk yield or composition. In conclusion, feeding a relatively small amount of AT (0.75 g/kg diet DM) with AN and FV reduced methane emission and yield by 9% and 12%, respectively, and there was no effect of feeding mixtures of AN and FV without AT. Feeding a higher level of AN with FV (5.85 g/kg DM) reduced milk urea concentration, suggesting inhibitory effects of phytotannins or other bioactive components on protein degradation.