PS4-28. Effects of Blanching Process and Supplementation Level of Undaria Pinnatifida Sporophyll on Nutrient Digestibility, Rumen Fermentation Characteristic, Methane Emission, and Rumen Microbiota In Vitro.

Abstract With increasing greenhouse gas (GHG) emissions, seaweeds have been extensively studied for their potential to mitigate GHG emissions in the rumen. Undaria pinnatifida (UP) is a brown alga widely consumed in Asia, whereas its sporophyll (UPS) is mostly wasted. This study aimed to evaluate the effects of blanching process and supplementation level of UPS on nutrient digestibility, fermentation characteristics, methane emissions, and microbial diversity in the rumen in vitro. UPS was washed at 15 °C (Non-blanched, NBLU) or 70 °C (Blanched, BLU) for 3 minutes. NBLU and BLU was supplemented at 0, 0.25%, 0.5%, and 1% of the basal diet, which was formulated for Hanwoo steers in growing period. Rumen buffer for in vitro incubation was prepared by mixing rumen fluid, collected from two cannulated Hanwoo heifers, with Van Soest medium at a 1:2 ratio. The diet in each experiment (0.3 g) was incubated with 40 mL of rumen buffer at 39 °C for 48 hours under anaerobic conditions. After incubation, total gas volume was measured and sub-sampled for greenhouse gas emissions (total gas, CO2, and CH4). Two milliliters of rumen buffer were collected for rumen microbial analysis. The remaining rumen buffer was centrifuged to separate residue for in vitro dry matter digestibility (IVDMD) and neutral detergent fiber digestibility (IVNDFD) and supernatant for rumen fermentation characteristics (pH, NH3-N, and VFA). Blanching process increased IVDMD (p = 0.001), and supplementation level decreased IVNDFD significantly (p = 0.045). Nonetheless, BLU 0.25% showed the highest values (p < 0.05) for both IVDMD and IVNDFD. Blanching process slightly decreased rumen pH (p = 0.001, 6.37 vs. 6.34). Total VFA concentration in 0.5% BLU was higher than that in 1% NBLU (p < 0.05, 86.5 vs. 55.4 mM/L). Propionate content increased (p < 0.05) by blanching process, but decreased butyrate content (p < 0.05). Propionate content was the highest in 0.25% BLU (p < 0.05, 22.8 % mol), whereas butyrate content was greatest in both CON and 1% BLU (p < 0.05, 17.25 % mol). Among the treatments, only 0.25% BLU significantly mitigated (p < 0.05) all types of GHG emissions (total gas, CO2, and CH4). Beta diversity analysis showed that NBLU group was clearly separated from the CON and BLU groups (p = 0.003), and diets supplemented with 0.25% and 0.5% UPS clustered distinctly compared to the CON group (p = 0.049). The relative abundance of Christensenellaceae_R-7_group, Succiniclasticum, Gastranaerophilales, and Treponema was varied by blanching process. In addition, the relative abundance of Christensenellaceae_R-7_group, NK4A214_group, and Treponema was affected by supplementation level. Therefore, it could be concluded that 0.25% BLU supplementation can improve in vitro nutrient digestibility and rumen fermentation characteristics, mitigate GHG emissions by modulating rumen microbiota. 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.