Seaweed as a supplement to ruminants winter diet - lessons learned

Seaweeds have been used as supplementary feed for livestock in Norway for centuries. Research activities on the use of seaweed as feed started early last century and continued until the late 1960s. The results were elusive, partly because the design of the experiments were imperfect. However, a long term experiment in the 1960’s demonstrated 6% higher milk production by cows supplemented mineral fortified Ascophyllum nodosum meal than in cows offered standard mineral supplement. The authors suggested that seaweed compounds might have had benficial effect on the rumen microflora. Seaweeds are a rich source of Se and antioxidants such as substituted phenols, polyphenols, vitamins, and vitamin precursors. Results from research last 10-20 years suggests that dietary supplementation with A. nodosum meal has positive effects on ruminant product quality and stress tolerance. Alginates have been documented to be non-specific immunostimulants. A. nodosum is currently commersially harvested and processed and sold as a feed supplement. Winter fed sheep and cattle in Norway needs to be given extra fat soluble vitamins and minerals, particularly vitamin E and Se, in order to ensure good animal health and production. Based on the aquired knowledge from international reseach on A. nodosum and its possible beneficial health effect, we tested if A. nodosum has immunestimulating effect and can be used as a substitute for synthetic vitamin E in sheep and cattle. Our hypothesis were that supplementing the diet with seaweed to sheep and lactating dairy cows would produce better adaptive immune response following immunization compared to no supplementation and similar to animals given extra vitamin E. Two feeding experiments were conducted, one continous with 40 pregnant ewes and one with 24 lactating dairy cows in a replicated Latin square design. The four supplement treatments applied were: A. Nodosum meal (SW), Natural vitamin E, Synthetic vitamin E, or Control. The average daily rate of A. Nodosum meal per ewe and cow in SW was 80 and 200 g DM, respectively. The ewes and their newborn lambs were monitored the entire indoor feeding period, from mating until pasture let out (200 d). In the ewes, supplementation with SW had no health effects compared to the other treatments, and serum IgG concentrations were reduced in the SW group.The adaptive immunity of the lambs was not affected by supplementation, and seaweed reduced the counts of different intestinal bacterial groups. However, seaweed interferred with the lambs passive immunity resulting in a mortality rate of 35 %, compared with 10% in Control. All cows responded well to immunization, but there were no significant effects of the diet on the immune response measured. The immunesupression observed in newborn lambs from ewes offered SW was likely du to impaired Ig absorption from colostrum, and we conclude that ruminants should not be supplemented with seaweed during peripartum. More research is needed on the identification of bioactive components in seaweed, their effects in animal health, the mechanisms related to their effects on the animal health and testing before seaweed should be used as a feed supplement to ruminants.