Amino acid profiles of nine seaweed species and their in situ degradability in dairy cows

The potential of seaweeds as alternative protein source was investigated in relation to their amino acid (AA) profiles and the ruminal and total tract digestibility of these AAs. Three red (Mastocarpus stellatus, Palmaria palmata, and Porphyra sp.), four brown (Alaria esculenta, Laminaria digitata, Pelvetia canaliculata, and Saccharina latissima), and two green (Cladophora rupestris. and Ulva sp.) seaweed species were used in this study (hereafter, referred to by Genus name only). All seaweeds were collected in Bodø, Northern Norway, during Spring and Autumn in 2014 and 2015, except Ulva, which was only sampled in Autumn of both years, and Saccharina which was not sampled in Spring 2014. All the samples were studied for AA concentration. Six species (Cladophora, Laminaria, Mastocarpus, Palmaria, Porphyra and Ulva) were selected for the more resource demanding in situ study. Species and season interactively affected the content of total AA in crude protein in different seaweeds investigated (P = 0.02), with values ranging from 67.2 for Laminaria in Spring to 90.2 gAA/16 g N for Ulva in Autumn. in situ AA degradability was also species specific. The seasonality of total AA in crude protein of different seaweed species mostly did not affect their ruminal degradability, except for alanine, while species and season interactively affected proline’s ruminal degradability. The total tract degradability showed that for Laminaria and Mastocarpus, methionine followed by leucine, isoleucine, histidine and lysine, were protected against rumen degradation. These protections seemed to be acid labile allowing digestion in the lower digestive tract. However, due to high indigestible fractions, these two seaweeds provided low amounts of AA to the intestines. Total tract AA digestibility values were the highest for Porphyra (906 g/kg) followed by Palmaria (843 g/kg) and the green seaweeds. To conclude, Laminaria and Mastocarpus are beneficial sources for bypass protein supply as they contain AA protected against rumen degradation. Based on their amount of AA and their AA degradability, Porphyra, followed by Palmaria and the green seaweeds (Ulva and Cladophora) can be considered as relevant sources of protein for ruminants.