Effects of <i>Hitoegusa</i> ( <i>Monostroma nitidum</i> ) Extracts on In Vitro Rumen Fermentation Profiles

In vitro rumen fermentations were conducted using extracts of the seaweed Hitoegusa (Monostroma nitidum), which contains rhamnan sulfate, as a fermentation substrate. This study examines the metabolic utilization of Hitoegusa extract by rumen microbiota through in vitro fermentation assays. In the first incubation, the addition of Hitoegusa extract led to increased gas production and total short-chain fatty acid (SCFA) concentrations, indicative of enhanced microbial activity and substrate fermentation. Alterations in SCFA profiles suggest a potential modulation of the rumen microbial community. In the second incubation, the incubation period was extended to 96 h, and gas production was measured. In any incubation period, gas production was increased in a dose-dependent manner. Supplementation with Hitoegusa extract to wheat starch did not result in a significant reduction in methanogenesis, possibly due to the limited biodegradability of rhamnan sulfate or an insufficient release of sulfate moieties. Further investigations are required to evaluate the degradability and bioavailability of rhamnan sulfate, isolate rumen bacteria capable of degrading this polysaccharide, and characterize the relevant enzymatic and genetic mechanisms. This study highlights the potential of underutilized marine macroalgae, such as Hitoegusa, as alternative feed resources for ruminant nutrition.