## 4 Discussion
Blanching seaweed with high-temperature tap water causes thermal shock, leading to cell rupture and the release of proteins and minerals from the cells. Elements like Na are found on the outer surface of the biomass, making them easier to remove rapidly during the blanching process [31]. [PERSON] et al. [32] reported that blanching kelp in water at 45 \({}^{\circ}\)C and 80 \({}^{\circ}\)C for 2 min reduced the levels of both Na and As. Additionally, blanching at 80 \({}^{\circ}\)C altered the ratio of Cr, Cu, Mn, and Zn compared to the raw kelp because the carboxyl group in alginic acid binds with minerals, making heavy metal accumulation relatively easy [33]. Blanching duration increased the in vitro digestibility of SH. This might be caused by the decreasing firmness of seaweed as the blanching time progresses, which indicates a thermal breakdown of polysaccharides in the seaweed cell walls [34]. Moreover, polysaccharides become gelatinized when heated to a temperature of 60 to 80 \({}^{\circ}\)C, improving their digestibility [35]. In the present study, in vitro digestibility decreased linearly as the supplementation levels increased at all times despite the blanching treatment. This may relate to the _Sargassum_ sp., which has lower digestibility than other seaweeds [36]. Additionally, alginate, which forms the cell wall of brown seaweed, could reduce nutrient digestibility [23,37]. Thus, this study suggests that increasing supplementation levels could decrease in vitro digestibility. The ruminal pH was unaffected by the SH supplementation levels and remained within the normal physiological range of 5.5 to 6.6 [23]. Most of the feed energy (about 70-80%) consumed by ruminants is converted into volatile fatty acids (VFA), which are absorbed by the ruminants and supply 80% of their energy requirements [35]. These findings align with previous studies that reported reductions in digestibility and VFA caused by SH supplements [36]. Almost all the propionate synthesis in the rumen occurs due to organisms producing succinate and other organisms that perform decarboxylation, turning succinate into propionate and CO\({}_{2}\). Since _F. succinogenes_ and _R. fluoresaciens_ produce succinate, which _S. ruminants_ converts into propionate, the production of succinate and propionate will likely decrease due to the sensitivity of these organisms to phlorotannins [38]. Methane production in the rumen involves a syntrophic relationship between H\({}_{2}\)-producing microbes and H\({}_{2}\)-consuming methanogens [39]. A reduction in rumen methanogenesis can sometimes convert fermentation from acetate to propionate, thereby favoring the propionate synthesis pathway over the acetate pathway [40]. Managing the H\({}_{2}\) sink is crucial for reducing methane in the rumen. As such, enhancing propionate production is a key strategy for methane mitigation because propionate acts as an H\({}_{2}\) sink, thereby decreasing H\({}_{2}\) availability for methanogens [41]. Recently, a study reported that methane gas in the rumen can be reduced by 50% by _Asparagopsis taxiformis_[11; 42]. In the present study, methane emission decreased as the SH supplementation levels increased, with the optimum SH supplementation for reducing methane emissions observed at 3%. These results are in accordance with several previous studies that reported reduced methane emissions with higher levels of seaweed supplementation in feed [10; 38; 43]. Furthermore, the most abundant polyphenols, such as phlorotannin, are suspected to be responsible for the methane-mitigating effects observed in SH. Phlorotannin is an abundant polyphenol in brown seaweed [44], comprising up to 15% of its dry matter [38]. Phlorotannin has the ability to reduce methane emissions through antioxidant activity [45]. It can decrease the activity of ciliated rumen protozoa, which are closely associated with methanogens and significant producers of the H\({}_{2}\) required for the conversion of CO\({}_{2}\) into methane.