Assessing in vivo digestibility and effects on immune system of sheep fed alfalfa hay supplemented with a fixed amount of Ulva rigida and Gracilaria vermiculophylla

Ruminants could be the most suitable domestic animals to be supplemented with seaweeds as the rumen ecosystem might provide the animal the ability to use these feed resources by breaking down the complex polysaccharides. The objective of the present in vivo study was to determine the digestibility and the effects on the immune system of one green ( Ulva rigida ) and one red ( Gracilaria vermiculophylla ) seaweed cultivated in an integrated multitrophic aquaculture system (IMTA) and included in the diet of sheep at a supplementing level up to 25%. Both seaweeds showed lower dry matter digestibilitity than alfalfa hay, the organic matter digestibility of U. rigida being higher than that of G. vermiculophylla . The studied seaweeds had similar fiber and energy digestibility. Seaweed supplementation did not influence hematological parameters, reactive oxygen species production by neutrophils, nor lymphocytic response to T and B cells mitogens. The low fiber digestibility of selected seaweeds would be the major constraint to their use in high amounts in ruminant diets. Dietary seaweed supplementation has no deleterious effect on the immune function of cells mediating innate and acquired immunity.