Effects of seasonal and interspecies differences in macroalgae procured from temperate seas on the Northern hemisphere on in vitro methane mitigating properties and rumen degradability

Enteric methane (CH4) from cattle constitutes a large proportion of the emission of anthropogenic greenhouse gasses. The objectives of this study were to investigate interspecies and seasonal variations in macroalgae, procured from the Northern Hemisphere, on CH4 production and rumen feed degradability in vitro. Corn silage or grass/clover silage (0.5 g), were incubated separately in buffered rumen fluid with addition of one of 22 different macroalgae (0.1 g), including both red, green, and brown species, hereof four brown species harvested at different seasons, resulting in an inclusion rate of 17 %. Rumen degradability of the pure macroalgae was determined by incubating macroalgae (0.5 g) without any basal feed. Accumulated gas production during 48 h of incubation was determined using the AnkomRF system equipped with airtight gasbags. Basal feeds without macroalgae addition served as controls, while the red macroalgae Asparagopsis taxiformis was included as a methane-inhibiting control. Each sample type was tested in triplicate in two separate runs. Amount of undegraded dry matter (DM) and organic matter (OM) after incubation was determined by filtration. Gas composition and concentration of volatile fatty acids (VFA) were determined by gas chromatography. Both A. taxiformis and Fucus serratus significantly reduced CH4 production, expressed per g DM, OM, degraded DM, and OM, when added to corn silage. Similar CH4 mitigating effect was observed when A. taxiformis was added to grass/clover silage, while F. serratus only significantly reduced the CH4 production expressed per g DM. None of the species included in the investigation of seasonal variations decreased CH4 production compared to the basal feeds. Palmaria palmata had the highest rumen degradability and associated VFA production, while F. vesiculosus and F. serratus had the numerically lowest rumen degradability and VFA production, respectively. In conclusion, F. serratus was the only Northern procurable macroalga showing CH4 mitigating potential, which depended on the nature of the basal feed.