Sammendrag
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.
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