Abstract/Summary

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 one of 4 treatments (10 per treatment) in blocks based on DIM, parity, BW, and milk yield. Treatments were a control TMR and one 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 free-stall 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 wks 5 to 7 of treatment, milk mineral concentrations were measured in wks 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), whilst 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 wk by treatment interaction in that cows fed the AN:FV mixture had higher milk iodine concentrations in wks 3 and 5 of the study. Cows fed the AN:FV also had lower milk urea concentration, suggesting effects of AN and/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.