PS6-6. Effects of Blanching Process and Supplementation Level of Fermented Codium Fragile on Rumen Fermentation and Greenhouse Gas Emission in vitro.

Abstract This study evaluated the effects of blanching process and supplementation level of fermented Codium fragile (COF) on in vitro rumen fermentation characteristics and greenhouse gas emissions. Fresh COF collected from Wando, South Korea, was washed in water at 15 °C (non-blanched, NBL) or 70 °C (blanched, BL) for 2 min to remove surface-attached impurities. The washed COFs (NBL or BL) were mixed with a grain mixture at a 1:4 ratio and ensiled for 30 d (FNBL vs. FBL). The ensiled COFs were supplemented at different levels (0 vs. 5 vs. 15 vs. 25%) of the basal diet. The fattening period diet for Hanwoo steers was used as a basal diet. Rumen fluid was collected from two cannulated Hanwoo heifers and mixed with Van Soest medium at a 1:2 ratio to make the rumen culture. Prepared rumen culture (30 mL) and experimental diets (0.3 g) in quadruplicate were placed in culture serum bottles (125 mL) and incubated anaerobically at 39 °C for 48 h. There were no effects on in vitro digestibility of dry matter (DMD) and organic matter (OMD) among the treatments. The FNBL resulted in greater total volatile fatty acid (VFA, p < 0.001) and acetate concentrations (p = 0.004) than FBL. Increasing supplementation levels reduced VFA concentration (p = 0.019). The gas production data showed that total gas production was not affected by the blanching process or supplementation level (p > 0.05). However, CO₂ emissions were lower in FBL than in FNBL when expressed on both DMD and OMD bases (p < 0.001). A similar trend was observed for CH4 emissions both in DMD and OMD, where FBL produced lower CH4 compared with FNBL (p < 0.001). In addition, the FBL treatment showed potential for reducing greenhouse gas emissions. Relative quantification analysis showed that FBL treatment reduced the abundance of methanogenic archaea and Methanobrevibacter smithii compared with FNBL (p < 0.01). In contrast, supplementation level significantly affected the abundance of methanogenic archaea, Methanobrevibacter ruminantium, Methanosarcina barkeri, Methanobrevibacter smithii, and Methanosphaera stadtmance (p < 0.05). Among the supplementation levels, 15% showed the most consistent reduction in methanogenic archaea abundance and methane emissions. These results indicate that supplementation of ensiled COF reduced methanogenic archaea abundance and methane emissions without negative effects on nutrient digestibility and rumen fermentation indices. Therefore, ensiled COF at 15% using the FBL treatment showed the greatest CH4 mitigation potential while maintaining feed utilization. For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text. For image description, please refer to the figure legend and surrounding text.