A descriptive chemical analysis of seaweeds, Ulva sp., Saccharina latissima and Ascophyllum nodosum harvested from Danish and Icelandic waters

•Seaweeds contain low levels of digestible nutrients for non-ruminants.•High ash and fiber concentrations in intact seaweeds may limit inclusion in feed.•Seaweeds may provide essential minerals.•Protein and fat fraction contain high EAA and EFA proportions.•Diverse monosaccharides in seaweed fibers indicate varying bioactive potential. This study aimed to discuss the chemical composition of three seaweed species commonly found in Nordic countries and its potential use in feed rations for pigs and calves. Two brown seaweeds Ascophyllum nodosum, Saccharina lastissima and a green seaweed Ulva sp. harvested from Danish and Icelandic waters were analyzed for proximate, amino acids, minerals, fatty acids and non-starch polysaccharides composition. All studied seaweeds contained low protein concentrations (i.e. 11.4–15.9 g/100 g DM). The ratio of essential amino acids (EAA) to non-essential amino acids (NEAA) was similar in all studied seaweeds (0.81−0.87). Ulva sp. had the highest ash concentration (48.2–54.4 g/100 g DM), followed by S. latissima (39.9 g/100 g DM) and A. nodosum (29.5 g/100 g DM). The most abundant macrominerals in the seaweeds were Ca, K and Na. Iodine was the most abundant micromineral in brown seaweeds (1.4–2.1 g/kg DM). Moreover, Ulva sp. had the highest Fe (5.1–8.0 g/kg DM), Mn (10.5 g/kg DM) and inorganic As (0.008 g/kg DM) concentrations. Ascophyllum nodosum had the highest crude fat concentration (3 g/100 g DM) and the highest concentration of polyunsaturated fatty acids (FAs) (37.9 g/100 g FA). Eicosapentaenoic acid (EPA) concentration was the highest in A. nodosum (7 g/100 g FA) followed by S. latissima (5 g/100 g FA) and Ulva sp. (2 g/100 g FA). Furthermore, concentration of α-linolenic acid, a precursor for EPA, was the highest in Ulva sp. (6.2–14.6 g/100 g FA). Total dietary fiber concentration was higher in the brown seaweeds (27.8–42.6 g/100 g DM) compared to the green seaweeds (17.9–21.5 g/100 g DM), where S. latissima had the highest soluble dietary fiber concentration. The high concentrations of ash and fiber may limit inclusion levels of the analyzed whole seaweeds in feed rations, mainly due to dilution of other nutrients in the feed, reduced digestibility of the feed and possible toxicities (i.e. high inorganic As). On the other hand, high concentrations of essential and valuable microminerals including I, Cu, Fe, Mn, Se were also detected in the studied seaweeds. High soluble dietary fiber concentration in S. latissima can