Mirka Thorsteinsson1,2,3, Annette Bruhn3,4, Martin Riis Weisbjerg1,2,3, Peter Lund1,2,3, and Mette Olaf Nielsen1,2,3
1Department of Animal and Veterinary Science, Aarhus University, Blichers Alle 20, Foulum, 8830 Tjele, Denmark
2iCLIMATE – Interdisciplinary Centre for Climate Change, Aarhus University, Denmark
3CBIO – Centre for Circular Bioeconomy, Aarhus University, Denmark
4Department of Ecoscience – Marine Ecology, C.F. Møllers Alle 4-6, 8000 Aarhus, Denmark
Rumen degradability (RD) of organic matter (OM) and contents of nitrogen (N) and ash are important for the nutritional value of being feeds for ruminants. Contents of N and ash vary considerably among seaweed species, with RD more sparsely documented. This study aimed to investigate N and ash contents and in vitro RD of 22 seaweed species procured from the Northern hemisphere, including both red, green, and brown seaweeds. Effects of harvest time were investigated in four of the species. Total N content was measured following the Dumas principle. Rumen degradability of seaweeds was analyzed by incubating 0.5 ± 0.02 g of seaweed with rumen inoculum, using the Ankom RF system. After 48 h of incubation, degradability of dry matter (DM) and OM were determined. In general, red species had the highest contents of N, ranging from 2.6-5.7% of DM, followed by brown and green species, ranging from 1.0-4.1% and 1.0-1.7%, respectively. Green species had the highest ash contents, 45.4 ± 9.2% of DM (mean ± SD), while brown species had the lowest contents, 31.9 ± 9.7%. Across species, brown species had significantly lower contents of degradable OM per g DM compared to red and green species. Harvest time did not affect N and ash contents or degradable OM per g DM across seasons. In conclusion, large variations in RD, and contents of N and ash were found between the species; however, some Nordic species show potential as future feeds for cattle.