Benefits of the red seaweed Asparagopsis taxiformis as an ingredient to manage methane (CH 4 ) emissions from the red meat and dairy industries continue to evolve. Asparagopsis has been demonstrated to eliminate enteric CH 4 emissions in vitro and reduce it greater than 80% in animals. Variability in animal studies is suspected to be associated with variable inclusion and proportions of grass and grain in the diet. This in vitro study aimed to elucidate effects of gradient grass to grain

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... ions in the fermentation using five steps from 100% Rhodes grass (RG) to 100% barley grain (BG). Gradient inclusion of Asparagopsis was in six steps of Control with no inclusion (C), Low (L), Low-Medium (LM), Medium (M), Medium-High (MH), and High (H) levels tested in three fermentation durations (24 h, 48 h, 72 h). There was significant effect of RG/BG and inclusion of Asparagopsis such that CH 4 production decreased with increasing Asparagopsis independent of RG/BG; however, there was enhanced reduction at greater proportions of BG. Thus, the level of Asparagopsis required to completely inhibit CH 4 production in vitro was decreased with decreasing RG/BG. Increasing the duration of fermentation had greatest effect on CH 4 at C, L, and LM levels of Asparagopsis independent of RG/BG, although magnitude of CH 4 production was greater for higher proportions of BG for the C and L levels. Digestibility of in vitro substrate increased with fermentation duration and increasing BG; however, there was no change associated with inclusion levels of Asparagopsis.